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PK-232 TECHNICAL MANUAL

APPENDIX A – AX.25 LEVEL 2 PROTOCOL

PK232TM Rev. A 5/87

A-3

Page 48

A.2.1

Flag Field

The flag field is one octet long. Since the flag is used to delimit frames, it occurs at both the begin-
ning and end of each frame. Two frames may share one flag, which would denote the end of the
first frame, and the start of the next frame. A flag consists of a zero followed by six ones followed
by another zero, or 01111110 (7E hex). As a result of bit stuffing (see

A.2.6

, below), this sequence

is not allowed to occur anywhere else inside a complete frame.

A.2.2

Address Field

The address field is used to identify both the source of the frame and its destination. In addition,
the address field contains the command/response information and facilities for level 2 repeater op-
eration. The encoding of the address field is described in

A.2.13

.

A.2.3

Control Field

The control field is used to identify the type of frame being passed and control several attributes
of the level 2 connection. It is one octet in length, and its encoding is discussed in

A.3.2.1

, below.

A.2.4

PID Field

The Protocol Identifier (PID) field shall appear in information frames (I and UI) only. It identifies
what kind of layer 3 protocol, if any, is in use.

The PID itself is not included as part of the octet count of the information field. The encoding of
the PID is as follows:

HEX

M L

S S

B B

Translation

0x01

00000001

ISO 8208/CCITT X.25 PLP

0x06

00000110

Compressed TCP/IP packet. Van Jacobson (RFC 1144)

0x07

00000111

Uncompressed TCP/IP packet. Van Jacobson (RFC 1144)

0x08

00001000

Segmentation fragment

**

yy01yyyy

AX.25 layer 3 implemented.

**

yy10yyyy

AX.25 layer 3 implemented.

0xC3

11000011

TEXNET datagram protocol

0xC4

11000100

Link Quality Protocol

0xCA

11001010

Appletalk

0xCB

11001011

Appletalk ARP

0xCC

11001100

ARPA Internet Protocol

0xCD

11001101

ARPA Address resolution

0xCE

11001110

FlexNet

0xCF

11001111

NET/ROM

0xF0

11110000

No layer 3 protocol implemented.

0xFF

11111111

Escape character. Next octet contains more Level 3 protocol information.

Where:

A

y

indicates all combinations used.

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Summary of Contents for PAKRATT PK-232

Page 1: ...TECHNICAL REFERENCE MANUAL MODEL PK 232 DATA CONTROLLER ADVANCED ELECTRONICS APPLICATIONS INC Preliminary Release ...

Page 2: ...quipment does cause interference to radio or TV reception which can be determined by turning the PK 232 on and off the user is encouraged to try and correct the interference using one or more of the following measures Reorient the antenna of the device receiving interference Relocate the computer with respect to this device Plug the computer into different outlet so the computer and the device are...

Page 3: ...Radio BATTERY BACK UP Your PK 232 uses batteries to back up the user programmable values in the system If you don t install batteries you ll have to re enter all of your personal system settings each time you turn on the PK 232 Your PK 232 will operate normally in all modes but will not retain your personalized pa rameters such as your call sign until you install three AA size batteries in the bat...

Page 4: ...1 1 Analog Section 2 1 10 2 1 2 Digital Section 2 1 10 2 1 3 Input Output Section 2 1 10 2 1 4 Display Section 2 1 10 2 1 5 Power Distribution 2 1 10 CHAPTER 3 THEORY OF OPERATION 3 1 System Diagrams 3 1 11 3 1 1 Block Diagrams 3 1 11 3 1 2 Logic Diagrams 3 1 11 3 1 3 Schematic Diagrams 3 1 11 3 2 Analog Subsystem 3 2 12 3 2 1 Receive Function 3 2 12 3 2 1 1 Receive Circuits 3 2 12 3 2 2 Transmit ...

Page 5: ...3 4 Call Sign Formats 4 7 24 4 4 Sending Data to the PK 232 4 8 25 4 4 1 Data Polling 4 8 25 4 4 2 The HPOLL Command 4 8 25 4 4 3 Special Case in AMTOR 4 9 26 4 4 4 Link Messages 4 9 26 4 5 Host Mode and Special Packet Applications 4 9 26 4 6 Raw HDLC 4 9 26 4 7 KISS TNC Asynchronous Packet Protocol 4 10 27 4 7 1 Starting KISS TNC Operation 4 11 28 4 7 2 KISS TNC Special Characters 4 11 28 4 7 3 K...

Page 6: ...bvious Problems 7 2 41 7 2 3 Assembly Problems 7 7 2 4 Cabling Problems 7 7 3 Specific Symptoms 7 7 3 1 Symptom Controller appears dead 7 7 3 2 Symptom Modem cannot be calibrated 7 4 43 7 3 3 Symptom Transmitter cannot be keyed 7 7 3 4 Symptom Transmitter signals not copyable by other stations 7 7 3 5 Symptom Received signals not copyable 7 7 4 Terminal Interface Troubleshooting 7 5 44 7 4 1 Sympt...

Page 7: ...o your terminal via an EIA standard RS 232 CCITT V 24 V 28 serial port and to your printer via a special Centronics type parallel interface Except for the printer interface the reverse proce dures convert ASCII data typed at your terminal to the signals and protocols required for transmission to other stations All necessary tone generation and demodulation modem functions are built in however exte...

Page 8: ...ol conversion Zilog Z 80 microprocessor RAM 16 kilobytes ROM Up to 48 kilobytes of ROM may be used Hardware HDLC Zilog 8530 SCC 1 4 4 Input Output Connections Radio Interface Two five pin TTL connectors selectable on the front panel Input output Lines Receive audio Transmit audio Push To Talk PTT External squelch input Ground External modem connector Five pin TTL TXD RXD DCD PTT Ground Direct FSK ...

Page 9: ...egment discriminator type bargraph indicator for HF tuning DCD LED Data Carrier Detect Status and Mode Indicators Mode Group Status Group BAUDOT STBY ASCII PHASE PKT IDLE MORSE ERROR CONV CHECK OVER FEC TFC TRANS ARQ RQ CMD MODE L CON STBY STA MULT SEND 1 4 6 General Power Requirements 13 VDC 12 to 16 VDC at 700 mA Mechanical Overall 11 8 25 2 5 279 4 209 6 63 5 mm Weight 3 pounds 1 36 kilograms ...

Page 10: ...solate the digital signals 2 1 3 Input Output Section The I O Section provides a standard serial data path in accordance with EIA RS 232 C and CCITT Recommendations V 24 V 28 between the PK 232 and the associated com puter or terminal The I O section contains an HDLC High Level Data Link Control translator output driv ers for AFSK tones DC logic voltages for direct FSK transmitter keying CW DC key...

Page 11: ...hows the digital logic por tion of the PK 232 which includes o the microprocessor o Read Only Memory ROM o Random Access Memory RAM o clock and control logic o part of the display logic o the logic associated with the digital communications between the PK 232 and the terminal The major portion of the power distribution section is also shown on this drawing 3 1 3 Schematic Diagrams Refer to the Sch...

Page 12: ...and in verted for passing to the internal modem circuitry When a full word of data eight bits has been assembled in the modem circuitry an inter rupt is generated to the microprocessor which then processes the data 3 2 1 1 Receive Circuits The received audio signals are routed through one of two radio connection receptacles J4 RADIO 1 or J6 RADIO 2 or through the respective paralleled radio input ...

Page 13: ...the Z8536 U6 The Z8536 translates the data into a binary string at the correct data rate and routes the binary string to AFSK generator U40 The AFSK generator supplies one of two tones to selected RADIO connector J4 or J6 depending on the position of RADIO 1 Radio 2 switch SW2 The transmit tone pair produced by the tone generator is selected by FET switch U35 This switch selects appropriate freque...

Page 14: ...and U5 3 3 3 8536 CIO Counter Timer and Parallel I O Unit U6 is an 8536 CIO chip which provides 20 parallel I O pins and three timers This chip re ceives address bits A0 A1 and A6 from the CPU The PK 232 s firmware addresses the 8536 by forcing all other address bits high yielding these addresses BC Parallel port A data BD Parallel port B data BE Parallel port C data BF Control port The 8536 uses ...

Page 15: ...AUDOT 0 1 0 0 CHECK 0 1 0 1 FEC 0 1 1 0 MODE L 0 1 1 1 ARQ 1 0 0 0 STBY 1 0 0 1 FAX 1 0 1 0 SIGNAL or SIAM PB3 drives the SEND LED through one of the 7406 drivers at U18 Parallel port B pins PB0 PB1 and PB2 drive the Status LED through the 7445 decoder at U12 PB2 PB1 PB0 LED 0 0 0 STBY 0 0 1 PHASE 0 1 0 OVER 0 1 1 IDLE 1 0 0 TFC TRANS 1 0 1 ERROR CONV 1 1 0 RQ CMD Parallel Port C drive their funct...

Page 16: ...ontrol 7D Terminal Port B data 7E HDLC Port A control 7F HDLC Port A data The 8530 chip has a 2 4576 MHz clock that is totally independent of the rest of the sys tem The serial interface signals TXD J2 pin 2 RTS 4 and DTR 20 flow from the RS 232 connector through the drivers on the 1489 chip at U19 to the 8530 s RXDB CTSB and DCDB pins respectively The 8530 output pins TXDB RTSB and DTRB pins are ...

Page 17: ...of divide by 2 and is brought out out to the U7 RTXCA input pin 12 as the 1 clock The RTSA output pin 17 is the PTT signal active low For the PTT to remain active for any length of time the DTRA output pin 16 must furnish a constantly oscillating signal This signal goes to the watchdog timer circuit Should the oscillating signal stop the PTT will go inactive after a period determined by the time c...

Page 18: ...ques other than AX 25 Level 2 Your program could be written to take much of the burden of operating a data controller and free you from the need to memo rize the PK 232 commands and possibly permit fully automatic system operation When working with conventional human oriented data controllers and Packet TNCs your hypothetical program must interpret and translate all the verbose human interface inf...

Page 19: ... first as shown below with the hexadecimal representation of each character listed above each its acronym or literal Note sp is the space bar character 11 18 03 48 4F 53 54 20 59 0D XON CAN COM H O S T sp Y CR Follow these steps 1 Send 01 A CTRL 2 Send the sequence 01 4F 47 47 17 3 If you receive the response 01 4F 47 47 00 17 you have successfully entered the Host mode If you receive some other r...

Page 20: ... the computer 4 1 6 Host Mode Recovery If it becomes necessary to quit Host mode because of a problem on the RS 232 link send any command with TWO SOH characters to start the block This makes sure the PK 232 goes to a known state where it is processing commands A suggestion 01 01 4F 47 47 17 SOH SOH O G G ETB 4 2 Host Computer Commands The host computer send blocks to the PK 232 using the CTL byte...

Page 21: ...E DC DCDCONN DL DELETE DF DFROM DI DISCONNE DW DWAIT EA EAS EC ECHO ES ESCAPE FA FAX FN FAXNEG FE FEC FL FLOW FR FRACK FS FSPEED FU FULLDUP GR GRAPHICS HB HBAUD HD HEADERLN HI HID HO HOST HP HPOLL ID ID IL ILFPAK IO IO JU JUSTIFY KI KISS LR LEFTRITE LO LOCK MX MAXFRAME MB MBX MC MCON MD MDIGI MM MEMORY MI MFILTER MF MFROM MH MHEARD MN MONITOR MO MORSE MP MSPEED MR MRPT MS MSTAMP MT MTO MA MYALIAS ...

Page 22: ...4 30 17 SOH CTL T D 4 0 ETB 4 2 6 SENDPAC To set SENDPAC to 0D send 01 4F 53 50 24 30 44 17 SOH CTL S P 0 D ETB 4 2 7 Interrogation or Querry Commands Querry commands are similar to the human or verbose mode in that the two letter com mand to the PK 232 is not followed by arguments that is the command is followed by ETB 4 3 PK 232 Responses The PK 232 always issues a response to each command o The...

Page 23: ...mand 08 VIA 09 not while connected 0A need MYCALL 0B need MYSELCAL 0C already connected 0D not while disconnected 0E different connects 0F too many packets outstanding 10 clock not set 11 need ALL NONE YES NO 15 not in this mode Other errors are SOH 5F X X W ETB bad block SOH 5F X X Y ETB bad CTL in block 4 3 1 Responses to Interrogation or Querry Commands Responses to query commands consist of th...

Page 24: ... v 30 if Standby x S if transmit 31 if Phasing R if receive 32 if Change over 33 if Idle 34 if Traffic 35 if Error 36 if RQ 37 if Sync yz present receive Morse code speed in words per minute 4 3 3 Link Status Request Response Use the CONNECT command to query the link state of channel x SOH 4x C O ETB The PK 232 response is SOH 4x C O a b c d e path ETB where a b c d and e are values 0 F ORed with ...

Page 25: ...PK 232 send the poll command as follows SOH 4F G G ETB If the PK 232 has nothing to send to the computer the response is SOH 4F G G 00 ETB If the PK 232 has data to send and information is waiting to be sent the response is shown below Only one block is sent for each poll SOH 2F ETB echoed data SOH 3x ETB data SOH 3F ETB monitored data SOH 4x ETB link status SOH 5x ETB link messages SOH 5x X X ETB...

Page 26: ...utput from CBELL Transmit data remaining 4 5 Host Mode and Special Packet Applications Certain differences exist when operating in Packet mode using the Host mode o Data is packetized only after the ETB character o PACTIME and CPACTIME are ignored The Host mode permits the use of special machine oriented interfaces that are inappropriate for direct interpretation by human users 4 6 Raw HDLC Raw HD...

Page 27: ...nting AX 25 see the AX 25 Link Layer Protocol document available from the ARRL Publications Department foe 10 4 7 KISS TNC Asynchronous Packet Protocol The PK 232 provides a simple asynchronous computer to TNC protocol for a Raw HDLC or KISS TNC developed by Phil Karn KA9Q The computer must again provide all AX 25 headers and timing functions KISS protocol is similar to the Raw HDLC protocol descr...

Page 28: ...eter value follows the CTL character o Each block ends with another FEND character The FESC Frame Escape character is the pass character o If any data character is a FEND that character is translated into the two byte se quence FESC TFEND Frame Escape Transposed Frame End o If any data character is a FESC that character is replaced by the two byte sequence FESC TFESC Frame Escape Transposed Frame ...

Page 29: ...before continuing Note that P 255 means always transmit as soon as possible regardless of the random number The result is that the TNC waits for an exponentially distributed random interval afr sensing that the channel has gone clear before attempting to transmit The idea here is that with proper tuning of the parameters P and SLOTTIME several stations with traffic to send are much less likely to ...

Page 30: ...ND where n is 00 for FULLDUP OFF and 01 for FULLDUP ON 4 7 4 6 HOST OFF CTL FF The HOST OFF command returns the PK 232 to the human or verbose mode HOST OFF has no arguments C0 FF C0 FEND CTL FEND 4 7 4 7 DATA CTL 00 The DATA block is used to send data from the computer to the PK 232 or from the PK 232 to the computer There is no data acknowledgement C0 00 data C0 FEND CTL FEND NOTE Data character...

Page 31: ...ters for a total of 648 bytes If CONMODE is CONVERSE linefeed characters may be appended to carriage re turns because ALFDISP is active Theoretically a packet contains 256 carriage re turns would result in a block of 136 256 256 or 648 bytes plus SOH CTL and ETB 4 9 MEMORY I O and ADDRESS Commands The Memory and I O commands work with the ADDRESS command to permit host access to the PK 232 s mmory...

Page 32: ...g of CONMODE o Do not send the CONVERSE or TRANS commands to the PK 232 o If CONMODE is CONV the parameters 8BITCONV ALFPACK ALFDISP LCOK and ESCAPE are active o If CONMODE is TRANS all characters are passed without modification These are the only differences between CONV and TRANS while in Host mode 4 11 MHEARD Command in Host mode The MH command has been altered in Host mode because the verbose ...

Page 33: ... release the contents are 86 07 29 4 13 Product Type Code The product type is available at EPROM location 0009 The byte return is bits 7 6 5 device bits 4 3 2 1 0 product 0 0 1 PK 80 0 0 0 0 1 PK 87 0 1 0 PK 87 0 0 0 1 0 PK 232 0 1 1 PK 232 0 0 0 1 1 PK 81T 1 0 0 UDC 232 0 0 1 0 0 PK 90 0 0 1 0 1 PK 80E 0 0 1 1 0 PK 87J 0 0 1 1 1 SPR 10A 0 1 0 0 0 PK 80I 0 1 0 0 1 HK 232 Previous software versions...

Page 34: ... break these wires The leads are long enough to allow the cover to be set on edge next to the chassis without disconnecting the wires from the board 5 2 Circuit Board Removal Refer to the Printed Circuit Board Drawing Figure 4 in APPENDIX C for the locations of the jumpers and other components o Remove the jumper from JP 1 to disconnect the battery backup voltage from the RAM circuit All preset pa...

Page 35: ...e front panel using the control washer and control nut o Turn the shaft of the control knob fully counterclockwise and place the knob on the shaft with the white index mark pointing to the R in the Word PAKRATT on the panel o Tighten the knob securely on the shaft o Place the cover edge next to the chassis and solder the black lead from the battery holder to the land closest to the switch assembly...

Page 36: ...alibration Procedure Refer to Figures 2 3 and 4 in APPENDIX C for circuit diagrams and printed circuit board component locations and also to APPENDIX D for sample signal waveforms The AFSK generator frequencies will be adjusted using the PK 232 s internal calibration rou tine and built in frequency meter An external frequency counter may also be connected at the junction of R160 and C59 Allow the ...

Page 37: ... dis play MYCALL was PK232 MYCALL now AAA 3 Type CAL followed by the RETURN key 4 Adjust R167 for a reading of 1200 10 Hz as display on the screen or frequency counter Use the SPACE BAR to toggle between mark and space If adjusting R167 has no effect press the SPACE BAR 5 Press the SPACE BAR 6 Adjust R165 for reading 2200 10 Hz as displayed on the screen or frequency counter 7 Press the H key to c...

Page 38: ... should be echoed back to the terminal 4 Type C CTRL C The monitor should display CMD 5 Type K RETURN to enter CONVERSE mode 6 Adjust the PK 232 s THRESHOLD control clockwise until the DCD LED on the PK 232 s front panel is lit Type several characters and a RETURN Observe the SEND LED on the front panel The SEND LED should NOT be lit 7 Adjust the THRESHOLD control counterclockwise until the DCD LE...

Page 39: ...just R155 AFSK output level to 10 millivolts peak to peak as measured at the junction of C59 and R160 16 Type C AEA RETURN The PK 232 responds CONNECTED TO AEA 17 Type a few characters and press RETURN 18 Type C The monitor should echo back CMD 19 Type D RETURN The monitor should respond DISCONNECTED This completes the functional tests ...

Page 40: ...ts can be done without the aid of an oscilloscope it will be required to verify signals at various points on the board if the problem cannot be located by visual means or with a meter Avoid short circuiting on integrated circuits when connecting meter or oscilloscope probes to the board It is good parctice to attach a secure ground wire to the meter or oscilloscope some point that cannot accidenta...

Page 41: ...ction often points to a problem or provides significant indications as to the controller s most suspect area Proceed to more specific analysis after completing the physical inspection and delaing with the apparent problem 7 3 1 Symptom Controller appears dead If the controller responds to initial power application with the MULT STA SEND and CON LEDs lit but fails to respond to any commands o Verif...

Page 42: ...30 DATA LINE D0 U1 Pin 14 ROM CHIP ENABLE CE U20 Pin 20 OUTPUT ENABLE OE U2 Pin 22 CE OE TIMING U2 Pin 20 U2 Pin22 READ LINE RD U1 Pin 21 WRITE LINE WR U1 Pin 22 PCLK U7 Pin 20 CLOCK TRXCA U7 Pin 14 CLOCK RTXCA U7 Pin 12 Each of these lines should show activity If any line is inactive this is a sign of trouble Logic lines that do not show activity can often be traced to a short circuit on the prin...

Page 43: ...s not copyable by other stations If other stations are unable to decode your transmissions when using FM o Verify the associated transmitter s modulation index Verify that peak deviation at any tone does not exceed 4 kHz o Adjust the AFSK output level with R155 to produce the correct transmitter deviation If other stations are unable to decode your transmission when using an SSB transmitter o Verf...

Page 44: ...n the controller are correct If the tests are valid verify the signal on U7 pin 27 with an oscilloscope o Recycle the power switch on the controller Transitions on this pin shortly after reset indicate that the controller is sending data o Verify that transitions are also present on U10 pin 1 7 4 2 Symptom Controller signs on with mutilated data If the terminal displays strange characters garbage ...

Page 45: ... settings are in ef fect the controller should echo typed characters back to the screen o Verify that U7 pin 21 shows a positive voltage level If not the fault could be in U19 If the above tests are valid o Type any keys on the terminal and verify that data is present on U7 pin 27 and U19 pin 1 If data is not seen the data is not reaching the controller from the terminal o Verify J2 the cable and ...

Page 46: ...r the various protocols in use or available to the amateur figure out the best and worst parts of each prtocol and see id the proto col could be enhanced to work properly over the amateur radio enviroment After reviewing the various protocols araund and talking with people in the computer networking industry we decided to push the AX 25 standard modified to allow a larger address field A about thi...

Page 47: ... protocol allows for the establishment of more than one link layer connection per device if the device is so capable This protocol does not prohibit self connections A self connection is consid ered to be when a device establishes a link to itself using its own address for both the source and destination of the frame Most link layer protocols assume that one primary or master device generally call...

Page 48: ... and control several attributes of the level 2 connection It is one octet in length and its encoding is discussed in A 3 2 1 below A 2 4 PID Field The Protocol Identifier PID field shall appear in information frames I and UI only It identifies what kind of layer 3 protocol if any is in use The PID itself is not included as part of the octet count of the information field The encoding of the PID is...

Page 49: ...ts Any time five contiguous one bits are sent the sending station shall in sert a zero bit after the fifth one bit During frame reception any time five contiguous one bits are received a zero bit immediately following five one bits shall be discarded A 2 7 Frame Check Sequence The frame check sequence FCS is a sixteen bit number calculated by both the sender and re ceiver of a frame It is used to ...

Page 50: ...ation that sent the frame These call signs are the call signs of the two ends of a level 2 AX 25 link only Fig 2 Nonrepeater Address Field Encoding First Octet Sent Address Field of Frame Destination Address Source Address A1 A2 A3 A4 A5 A6 A7 A8 A9 A10 A11 A12 A13 A14 A1 through A14 are the fourteen octets that make up the two address subfields of the address field The destination subaddress is s...

Page 51: ... set the receive sequence number N R is 1 the send sequence number N S is 7 A 2 13 1 1 Destination Subfield Encoding Fig 3 shows how an amateur call sign is placed in the destination address subfield occupying oc tets A1 thru A7 Fig 3 Destination Field Encoding Octet ASCII Bin Data Hex Data A1 W 10101110 AE A2 B 10000100 84 A3 4 01101000 68 A4 J 10010100 94 A5 F 10001100 8C A6 I 10010010 92 A7 SSI...

Page 52: ...the destination and source address subfields except for the most significant bit in the last octet called the H bit The H bit is used to indicate whether a frame has been re peated or not In order to provide some method of indicating when a frame has been repeated the H bit is set to zero on frames going to a repeater The repeater will set the H bit to one when the frame is re transmitted Stations...

Page 53: ...tocol allows operation through more than one repeater creating a primi tive frame routing mechanism Up to eight repeaters may be used by extending the repeater ad dress subfield When there is more than one repeater address the repeater address immediately following the source address subfield will be considered the address of the first repeater of a multi ple repeater chain As a frame progresses t...

Page 54: ... maintain proper link control The control fields used in AX 25 use the CCITT X 25 control fields for balanced operation LAPB with an additional control field taken from ADCCP to allow connectionless and round table opera tion There are three general types of AX 25 frames They are the Information frame I frame the Supervisory frame S frame and the Unnumbered frame U frame Fig 5 shows the basic form...

Page 55: ...mes They are also responsible for establishing and terminating link connections U frames also allow for the transmission and reception of information outside of the normal flow control Some U frames may contain information and PID fields The P F bit is used as described in A 4 2 A 3 2 2 Control Field Parameters A 3 2 3 Sequence Numbers Every AX 25 I frame shall be assigned modulo 8 a sequential nu...

Page 56: ...he DXE A 3 4 1 Information Command Frame Control Field The function of the information I command is to transfer across a data link sequentially num bered frames containing an information field The information frame control field is encoded as shown in Fig 6 These frames are sequentially numbered by the N S subfield to maintain control of their passage over the link layer connection Fig 6 I frame c...

Page 57: ...end of the link can be requested by sending a RNR command frame with the P bit set to one A 3 4 2 3 Reject REJ Command and Response The reject frame is used to request retransmission of I frames starting with N R Any frames that were sent with a sequence number of N R 1 or less are acknowledged Additional I frames may be appended to the retransmission of the N R frame if there are any Only one rej...

Page 58: ... sending the offending frame again Typically this condition will appear when a frame without an FCS error has been received with one of the following conditions 1 The reception of an invalid or not implemented command or response frame 2 The reception of an I frame whose information field exceeds the agreed upon length See A 4 7 3 below 3 The reception of an improper N R This usually happens when ...

Page 59: ...used the reject condition was considered invalid because it was a U or S frame that had an information field that is not allowed Bit W must be set to 1 in addition to the X bit 7 If Y is set to 1 the control field received and returned in bits exceeded the maximum allowed under this recommendation in A 4 7 3 below 8 If A is set to 1 the control field received and returned in bits 1 to 8 contained ...

Page 60: ...wise error free received frame does not match the receive state variable V R a send sequence error has occurred and the information field will be discarded The receiver will not acknowledge this frame or any other I frames until N S matches V R The control field of the erroneous I frame s will be accepted so that link supervisory functions such as checking the P F bit can still be performed Becaus...

Page 61: ...1 1 Address Information All transmitted frames shall have address fields conforming to A 2 13 above All frames shall have both the destination device and the source device addresses in the address field with the destina tion address coming first This allows many links to share the same RF channel The destination address is always the address of the station s to receive the frame while the source a...

Page 62: ...sponse frame with the F bit set to 1 The next response frame returned to a S or I command frame with the P bit set to 1 received in the disconnected state will be a DM response frame with the F bit set to 1 The P bit is used in conjunction with the time out recovery condition discussed in A 3 5 4 above When not used the P F bit is set to zero A 4 3 Procedures For Link Set Up and Disconnection A 4 ...

Page 63: ...e A 4 7 A 4 3 3 2 A DXE upon receiving a valid DISC command shall send a UA response frame and enter the dis connected state A DXE upon receiving a UA or DM response to a sent DISC command shall can cel timer T1 and enter the disconnected state A 4 3 3 3 If a UA or DM response is not correctly received before T1 times out the DISC frame should be sent again and T1 restarted If this happens N2 time...

Page 64: ...ero All SABM and DISC frames should be sent with the P bit set to one This will prevent any confusion when a DM frame is received A 4 3 6 Connectionless Operation In Amateur Radio there is an additional type of operation that is not feasible using level 2 connec tions This operation is the round table where several amateurs may be engaged in one conversa tion This type of operation cannot be accom...

Page 65: ...ng the received frame Alternately the device may send a RR frame with N R equal to V R and then send the I frame 2 If there are no outstanding I frames the receiving device will send a RR frame with N R equal to V R The receiving DXE may wait a small period of time before sending the RR frame to be sure additional I frames are not being transmitted A 4 4 2 2 If the DXE is in a busy condition it ma...

Page 66: ...r S frame and then retransmit the I frame s 3 If the DXE is operating in a full duplex channel transmitting another I frame when it receives a REJ frame it may abort the I frame it was sending and start retransmission of the requested I frames immediately 4 The DXE may send just the one I frame outstanding or it may send more than the one indi cated if more I frames followed the first one not ackn...

Page 67: ...hen a frame is received with the correct FCS and address field during the information transfer state with one or more of the conditions in A 3 4 3 3 above Under these conditions the DXE will ask the other DXE to reset the link by transmitting a FRMR re sponse as outlined in A 4 6 3 below After sending the FRMR frame the sending DXE will enter the frame reject condition This condi tion is cleared w...

Page 68: ...aintain the integrity of the AX 25 level 2 connection use of these timers is recommended A 4 7 1 1 Acknowledgement Timer T1 The first timer T1 is used to make sure a DXE doesn t wait forever for a response to a frame it sends This timer cannot be expressed in absolute time since the time required to send frames varies greatly with the signaling rate used at level 1 T1 should take at least twice th...

Page 69: ...ally defined and depends greatly on level 1 operation T3 should be greater than T1 and may be very large on channels of high in tegrity A 4 7 2 Maximum Number of Retries N2 The maximum number of retries is used in conjunction with the T1 timer A 4 7 3 Maximum Number of Octets in an I Field N1 The maximum number of octets allowed in the I field will be 256 There shall also be an integral number of ...

Page 70: ...ssible from the TNC software giving the attached host complete control over and access to the contents of the HDLC frames transmitted and received over the air This is central to the KISS philosophy the host software should have control over all TNC functions at the lowest possible level The AX 25 protocol is removed entirely from the TNC as are all command interpreters and the like The TNC simply...

Page 71: ...a buffer containing the current frame Receiving a FEND marks the end of the current frame Receipt of a FESC puts the receiver into escaped mode causing the receiver to translate a following TFESC or TFEND back to FESC or FEND respectively before adding it to the receive buffer and leaving escaped mode Receipt of any character other than TFESC or TFEND while in escaped mode is an error no action is...

Page 72: ...FCS has been sent in 10 ms units This command is obsolete and is included here only for compatibility with some existing implementations 5 FullDuplex The next byte is 0 for half duplex nonzero for full duplex The default is 0 i e half duplex 6 SetHardware Specific for each TNC In the TNC 1 this command sets the modem speed Other implementations may use this function for other hard ware specific fu...

Page 73: ... tive in the meantime the TNC again waits for it to clear before continuing Note that p 1 means transmit as soon as the channel clears in this case the p persistence algorithm degenerates into the 1 persistent CSMA generally used by conventional AX 25 TNCs p persistence causes the TNC to wait for an exponentially distributed random interval after sensing that the channel has gone clear before atte...

Page 74: ...ode without ROM changes Since the TNC 1 and TNC 2 KISS versions were written by different authors than the original AX 25 firmware and because the original source code for those TNCs was not made available running KISS on these TNCs requires the in stallation of nonstandard ROMs Two ROMs are available for the TNC 2 One contains dedicated KISS TNC code the TNC operates only in the KISS mode The dow...

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