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18

®

ADS7806

SPI INTERFACE

The SPI interface is generally only capable of 8-bit data
transfers. For some microcontrollers with SPI interfaces, it
might be possible to receive data in a similar manner as
shown for the QSPI interface in Figure 12. The
microcontroller will need to fetch the 8 most significant bits
before the contents are overwritten by the least significant
bits.

A modified version of the QSPI interface shown in Figure 13
might be possible. For most microcontrollers with SPI inter-
face, the automatic generation of the start-of-conversion
pulse will be impossible and will have to be done with
software. This will limit the interface to ‘DC’ applications
due to the insufficient jitter performance of the convert pulse
itself.

DSP56000 INTERFACING

The DSP56000 serial interface has an SPI compatibility
mode with some enhancements. Figure 14 shows an inter-
face between the ADS7806 and the DSP56000 which is very
similar to the QSPI interface seen in Figure 12. As men-
tioned in the QSPI section, the DSP56000 must be pro-
grammed to enable the interface when a LOW to HIGH
transition on SC1 is observed (BUSY going HIGH at the end
of conversion).
The DSP56000 can also provide the convert pulse by includ-
ing a monostable multi-vibrator as seen in Figure 15. The
receive and transmit sections of the interface are decoupled
(asynchronous mode) and the transmit section is set to
generate a word length frame sync every other transmit
frame (frame rate divider set to two). The prescale modulus
should be set to five.

The monostable multi-vibrator in this circuit will provide
varying pulse widths for the convert pulse. The pulse width
will be determined by the external R and C values used with
the multi-vibrator. The 74HCT123N data sheet shows that

the pulse width is (0.7)RC. Choosing a pulse width as close
to the minimum value specified in this data sheet will offer
the best performance. See the Starting A Conversion sec-
tion of this data sheet for details on the conversion pulse
width.

The maximum conversion rate for a 20.48MHz DSP56000
is 35.6kHz. If a slower oscillator can be tolerated on the
DSP56000, a conversion rate of 40kHz can be achieved by
using a 19.2MHz clock and a prescale modulus of four.

FIGURE 15. DSP56000 Interface to the ADS7806. Processor Initiates Conversions.

R

EXT1

C

EXT1

Q1

B1

CLR1

A1

R/C

DATACLK

SDATA

CS

EXT/INT

BYTE

ADS7806

74HCT123N

SC2

SC0

SRD

DSP56000

SYN = 0 (Asychronous)
GCK = 1 (Gated clock)
SCD2 = 1 (SC2 is an output)
SHFD = 0 (Shift MSB first)
WL1 = 0 WL0 = 1 (Word length = 16 bits)

R

+5V

C

+5V

R/C

BUSY

SDATA

DATACLK

CS

EXT/INT

BYTE

ADS7806

SC1

SRD

SCO

DSP56000

SYN = 0 (Asychronous)
GCK = 1 (Gated clock)
SCD1 = 0 (SC1 is an input)
SHFD = 0 (Shift MSB first)
WL1 = 0 WL0 = 1 (Word length = 12 bits)

Convert Pulse

FIGURE 14. DSP56000 Interface to the ADS7806.

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Содержание PCM-A/D-12

Страница 1: ...OPERATIONS MANUAL PCM A D 16 PCM A D 12 WinSystems reserves the right to make changes in the circuitry and specifications at any time without notice Copyright 1996 by WinSystems All Rights Reserved...

Страница 2: ...REVISION HISTORY P N 403 0230 000 ECO Number Date Code Rev Level Originated 960206 B 97 31 970513 B1 WinSystems The Embedded Systems Authority...

Страница 3: ...Selection 2 3 2 6 Input Connector Pin Definitions 2 8 2 7 PC 104 Bus Pin Definitions 2 8 2 8 Connector Jumper Summary 2 9 3 PCM A D Programming Reference 3 1 I O Register Definitions 3 1 3 2 Conversi...

Страница 4: ...6 and PCM A D 12 are low cost general purpose successive approxi mation analog to digital converters The PCM A D 16 uses the Burr Brown ADS7807 16 bit converter while the PCM A D 12 uses the Burr Brow...

Страница 5: ...5mA typ w o DC DC converter installed 1 3 2 Mechanical Dimensions 3 6 X 3 8 X 0 6 PC Board FR4 Epoxy glass with 2 signal layers and 2 power planes with screened component legend and plated through ho...

Страница 6: ...l Time Technical Support may also be requested by FAX at 817 548 1358 The PCM A D has 16 single ended inputs or 8 differential inputs and converts in 25 30uS The end of conversion can be determined in...

Страница 7: ...The end of conversion interrupt may be routed to any unused PC 104 interrupt line us ing the jumper block at J9 The illustration below shows the relationship between the jumper position and the interr...

Страница 8: ...lled or damage to the PCM A D board other PC 104 modules the CPU board or the power supply may result Boards provided with DC DC converters from the factory will not have the jumper posts installed at...

Страница 9: ...to the following table Full Scale Range 0 0 5 0 Volts Least Significant Bit LSB 76uV 16 Bit or 1 22mV 12 Bit Full Scale FS 1LSB 4 999924V 16 Bit or 4 99878V 12 Bit FFFFH Midscale 2 50V 8000H One LSB...

Страница 10: ...table Full Scale Range 10 0V Least Significant bit 305uV 16 Bit or 4 88mV 12 Bit Full Scale FS 1LSB 9 999695V 16 Bit or 9 99512 12 Bit 7FFFH Midscale 0 0V 0000H One LSB below Midscale 305uV 16Bit or...

Страница 11: ...5 0 Volts Least Significant Bit LSB 76uV 16 Bit or 1 22mV 12 Bit Full Scale FS 1LSB 4 999924V 16 Bit or 4 99878V 12 Bit FFFFH Midscale 2 50V 8000H One LSB Below Midscale 2 4999924V 16 Bit or 2 49878...

Страница 12: ...g this mode Two s complement binary values are read from the converter per the following table Full Scale Range 10 0V Least Significant bit 305uV 16 Bit or 4 88mV 12 Bit Full Scale FS 1LSB 9 999695V 1...

Страница 13: ...nded Input Channels Differential Input Channels B1 o o A1 B2 o o A2 B3 o o A3 B4 o o A4 B5 o o A5 B6 o o A6 B7 o o A7 B8 o o A8 B9 o o A9 B10 o o A10 B11 o o A11 B12 o o A12 B13 o o A13 B14 o o A14 B1...

Страница 14: ...nector 2 8 J4 Input range select jumper 2 3 J5 Mode select differential vs single ended 2 3 J6 DC DC Converter Enable 2 3 J7 Mode Select binary vs two s complement 2 3 J8 I O Address Select 2 2 J9 Int...

Страница 15: ...t Only MSB Data BASE 3 Reserved Reserved Each Register will be examined in more detail 3 1 1 Base Address Write Register Channel Select D7 N A D6 N A D5 N A D4 N A D3 Bit 3 of select nibble D2 Bit 2 o...

Страница 16: ...0 of select nibble Writing a value to the BASE 1 I O address not only selects the channel number as en coded in bits 3 0 but after a hardware settling delay of approximately 6uS starts a conver sion T...

Страница 17: ...he Channel Select Start Conver sion register This method of starting the converter allows for maximum throughput when repetitively converting on the same channel as no multiplexer settling time is req...

Страница 18: ...BASE_ADDRESS 0x110 unsigned convert int channel_number unsigned return_value Start the conversion by writing to the Select Start conversion Register outportb BASE_ADDRESS 1 channel_number Now wait for...

Страница 19: ...5 WinSystems The Embedded Systems Authority Channel RAW HIGH LOW DATA CURRENT MAX MIN VOLTAGE Number DATA DATA DATA DEV VOLTAGE VOLTAGE VOLTAGE DEVIATION 00 FFFF FFFF FFFF 0000 5 0000 5 0000 5 0000 0...

Страница 20: ...it and 16 bit M Toggle the conversion mode This key toggles the conversion mode between Interrupt Mode and Polled Mode When in the Interrupt Mode a counter in the lower right corner will display the n...

Страница 21: ...ey 7 Adjust R4 counter clockwise for a reading corresponding to the input source Some lower bit deviation may be experienced and is normal 8 Set the input source to 5 00 volts Hit R to clear the curre...

Страница 22: ...4 APPENDIX A PCM A D Parts Placement Guide...

Страница 23: ...5 APPENDIX B PCM A D Parts List...

Страница 24: ...45 002 IC 74HCT245DW SM U7 I 1 0 2 611 0221 002 IC 74HC221D SO 16 U8 I 1 0 2 612 0688 002 IC 74HCT688AF SM U9 I 1 0 2 200 0064 100 SCKT 64 POS STK QPHF2 64 020 1Z PLAST J10 CLIP PIN B10 MUST BE HAND S...

Страница 25: ...UT HEX NYLON 4 40 I 2 0 2 525 0304 001 SIZE 3 COIN ENVLPE 2 5 X 4 25 50260 SIZE 3 COIN ENVELOPE 2 1 2 X 4 1 4 I 1 0 SUB ASSEMBLY TOTAL KIT PCM STANDOFF 2 ARLIN 6 Items TOP ASSEMBLY TOTAL PCM A D12 16...

Страница 26: ...6 APPENDIX C BURR BROWN ADS7806 ADS7807 Datasheet Reprint...

Страница 27: ...re range CDAC 6k 40k 10k BUSY Parallel and Serial Data Out Comparator Buffer 20k R1IN R2IN REF Successive Approximation Register and Control Logic Clock Power Down BYTE CS R C 40k Internal 2 5V Ref Re...

Страница 28: ...LSB Gain Error 0 2 0 1 Full Scale Error 3 4 0 5 0 25 Full Scale Error Drift 7 5 ppm C Full Scale Error 3 4 Ext 2 5000V Ref 0 5 0 25 Full Scale Error Drift Ext 2 5000V Ref 0 5 ppm C Bipolar Zero Error...

Страница 29: ...og input is acquired to rated accuracy A Convert Command after this delay will yield accurate results 6 All specifications in dB are referred to a full scale input 7 Usable Bandwidth defined as Full S...

Страница 30: ...ata bit 7 if BYTE is LOW Hi Z when CS is HIGH and or R C is LOW 14 DGND Digital Ground 15 D2 O LOW if BYTE is HIGH Data bit 6 if BYTE is LOW Hi Z when CS is HIGH and or R C is LOW 16 D1 O LOW if BYTE...

Страница 31: ...OISE DISTORTION vs TEMPERATURE fIN 1kHz 0dB fS 10kHz to 40kHz 74 0 73 9 73 8 73 7 73 6 75 50 25 0 25 50 75 100 125 150 Temperature C SINAD dB A C PARAMETERS vs TEMPERATURE fIN 1kHz 0dB 110 105 100 95...

Страница 32: ...Percent From Ideal mV From Ideal ENDPOINT ERRORS UNIPOLAR RANGES Temperature C 75 50 25 0 25 50 75 100 125 150 Percent From Ideal All Codes INL UPO Error FS Error 4V Range FS Error 5V Range FS Error...

Страница 33: ...will be valid on both the rising and falling edges of the data clock BUSY going HIGH can be used to latch the data All convert commands will be ignored while BUSY is LOW The ADS7806 will begin tracki...

Страница 34: ...lel data in Straight Binary or Binary Two s Complement data output format If SB BTC pin 7 is HIGH the output will be in SB format and if LOW the output will be in BTC format Refer to Table V for ideal...

Страница 35: ...tput tie EXT INT pin 8 HIGH and DATACLK pin 18 LOW SDATA pin 19 should be left unconnected The parallel output will be active when R C pin 22 is HIGH and CS pin 23 is LOW Any other combination of CS a...

Страница 36: ...ted or during conversion n 1 An obvious way to simplify control of the converter is to tie CS LOW and use R C to initiate conversions While this is perfectly acceptable there is a possible problem whe...

Страница 37: ...xternal Clock EXT INT Tied HIGH Read after Conversion EXTERNAL DATACLK CS 0 Bit 11 MSB R C BUSY SDATA TAG 1 2 3 11 12 13 14 Bit 10 Bit 1 Bit 0 LSB Tag 0 Tag 1 Tag 1 Tag 2 Tag 11 Tag 12 Tag 13 Tag 14 T...

Страница 38: ...onous data clock can cause digital feedthrough degrading the converter s perfor mance Refer to Table VI and Figure 6 TAG FEATURE TAG Pin 20 inputs serial data synchronized to the external or internal...

Страница 39: ...l yield either positive full scale or negative full scale digital outputs respectively There will be no wrapping or folding over for analog inputs outside the nominal range CALIBRATION HARDWARE CALIBR...

Страница 40: ...er which reduces the input signal to a 0 3125V to 2 8125V input range at the CDAC The internal resistors are laser trimmed to high relative accuracy to meet full specifi cations The actual input imped...

Страница 41: ...an internal buffer for the reference voltage See Figure 10 for characteristic impedances at the input and output of the buffer with all combinations of power down and reference down REF REF pin 5 is a...

Страница 42: ...ca tions the ADS7806 uses 90 of its power for the analog circuitry The ADS7806 should be considered as an analog component The 5V power for the A D should be separate from the 5V used for the system s...

Страница 43: ...data input of the microcontroller is tied to the MSB D7 of the ADS7806 instead of the serial output SDATA Using D7 instead of the serial port offers tri state capability which allows other peripheral...

Страница 44: ...and transmit sections of the interface are decoupled asynchronous mode and the transmit section is set to generate a word length frame sync every other transmit frame frame rate divider set to two The...

Страница 45: ...25 s max while consuming only 35mW max Laser trimmed scaling resistors provide standard industrial input ranges of 10V and 0V to 5V In addition a 0V to 4V range allows develop ment of complete single...

Страница 46: ...4V Ranges 3 mV Unipolar Zero Error Drift 0V to 5V 0V to 4V Ranges 0 5 ppm C Recovery Time to Rated Accuracy 2 2 F Capacitor to CAP 1 ms from Power Down 5 Power Supply Sensitivity 4 75V VS 5 25V 8 LSB...

Страница 47: ...o rated accuracy A Convert Command after this delay will yield accurate results 6 All specifications in dB are referred to a full scale input 7 Usable Bandwidth defined as Full Scale input frequency a...

Страница 48: ...sion With CS LOW a rising edge on R C enables the parallel output 23 CS I Internally OR d with R C If R C is LOW a falling edge on CS initiates a new conversion If EXT INT is LOW this same falling edg...

Страница 49: ...0 1k 10k 100k 1M 100 80 90 70 60 50 40 30 20 10 SINAD dB TYPICAL PERFORMANCE CURVES At TA 25 C fS 40kHz VDIG VANA 5V using internal reference and fixed resistors shown in Figure 7b unless otherwise sp...

Страница 50: ...25 C fS 40kHz VDIG VANA 5V using internal reference and fixed resistors shown in Figure 7b unless otherwise specified 3 2 1 0 1 2 3 16 Bit LSBs 0 65535 57344 49152 40960 32768 24576 16384 8192 Decimal...

Страница 51: ...stay LOW until the conversion is completed and the output register is updated If BYTE pin 21 is LOW the 8 most significant bits will be valid when BUSY rises if BYTE is HIGH the 8 least significant b...

Страница 52: ...f control pins CS can be tied LOW using R C to control the read and convert modes This will have no effect when using the internal data clock in the serial output mode However the parallel output and...

Страница 53: ...el Outputs Hi Z State BUSY R C DATA BUS High Byte t3 t4 t21 t21 t1 t21 t21 BYTE t21 t21 t21 t21 t21 t21 Hi Z State Low Byte Hi Z State t9 t12 t9 t12 CS FIGURE 2 Conversion Timing with Parallel Output...

Страница 54: ...So with CS LOW either R C and or DATACLK must be LOW during this period to avoid losing valid data SERIAL OUTPUT Data can be clocked out with the internal data clock or an external data clock When usi...

Страница 55: ...External Clock EXT INT Tied HIGH Read after Conversion EXTERNAL DATACLK CS 0 Bit 15 MSB R C BUSY SDATA TAG 1 2 3 4 16 17 18 Bit 14 Bit 1 Bit 0 LSB Tag 0 Tag 1 Tag 1 Tag 2 Tag 15 Tag 16 Tag 17 Tag 18 T...

Страница 56: ...onous data clock can cause digital feedthrough degrading the converter s perfor mance Refer to Table VI and Figure 6 TAG FEATURE TAG Pin 20 inputs serial data synchronized to the external or internal...

Страница 57: ...s for Hardware Calibration see Figure 7a 200 1 2 3 4 5 6 AGND2 REF CAP R2IN AGND1 R1IN 2 2 F 2 2 F 33 2k 100 VIN 200 1 2 3 4 5 6 AGND2 REF CAP R2IN AGND1 R1IN 2 2 F 2 2 F 100 5V 66 5k VIN 200 1 2 3 4...

Страница 58: ...transfer functions which occur when the external resistors are removed To further analyze the effects of removing any combination of the external resistors consider Figure 9 The combination of the ex...

Страница 59: ...the SNR and SINAD The REF pin should not be used to drive external AC or DC loads See Figure 10 The range for the external reference is 2 3V to 2 7V and determines the actual LSB size Increasing the r...

Страница 60: ...upply All the ground pins of the A D should be tied to an analog ground plane separated from the system s digital logic ground to achieve optimum performance Both analog and digital ground planes shou...

Страница 61: ...6 will yield the 3 distribution or 99 7 of all codes Statistically up to 3 codes could fall outside the 5 code distribution when executing 1000 conversions The ADS7807 has a TN of 0 8 LSBs which yiel...

Страница 62: ...ansfer In addition CPOL and CPHA should be set to zero SCK normally LOW and data captured on the rising edge The command control byte for the eight bit transfer should be set to 20H and for the sixtee...

Страница 63: ...d length 16 bits Convert Pulse width as close to the minimum value specified in this data sheet will offer the best performance See the Starting A Conversion section of this data sheet for details on...

Страница 64: ...7 APPENDIX D PCM A D Demo Software Source Listing...

Страница 65: ...ample source code on an as is basis and makes no warranty as to fitness of purpose In no event shall WinSystems be liable for consequential incidental or special damages of any kind through the use of...

Страница 66: ...pt_count 0 int mode 0 Program entry point void main unsigned char lsb msb char c unsigned low high current int channel channel_number 0 To start we will install our interrupt handler saving the old ha...

Страница 67: ...y mode dependent screen information gotoxy 1 25 switch mode case 0 printf Scale 0 to 5 Volts Single Ended break case 1 printf Scale 10 to 10 Volts Single Ended break case 2 printf Scale 0 to 5 Volts D...

Страница 68: ...keys recognized are r reset deviation values t toggle voltage mode m toggle betweent interrupt and polled mode c getch if c r for channel 0 channel max_channel channel flag channel 0 else if c t mode...

Страница 69: ...t s value if interrupt_mode outportb AD_BASE 1 channel Start the conversion wait_complete wait for the channel to complete lsb inportb AD_BASE 1 assemble the word result msb inportb AD_BASE 2 from the...

Страница 70: ...t_val printf 8 4f float low_val channel 0x8000 float full_count full_scale offset_val printf 8 4f float high_val channel 0x8000 low_val channel 0x8000 float full_count full_scale else printf 8 4f floa...

Страница 71: ...the arrays for display by the foreground routine void interrupt ad_isr int temp unsigned char lsb msb unsigned current interrupt_count temp channel_number lsb inportb AD_BASE 1 msb inportb AD_BASE 2 c...

Страница 72: ...val temp 0x8000 high_val temp current else if current low_val temp low_val temp current if current high_val temp high_val temp current Send the EOI to the interrupt controller to re arm for next inter...

Страница 73: ...8 APPENDIX E PCM A D Schematic Diagrams...

Страница 74: ...2 5V DRQ2 12V OWS 12V GND SMEMW SMEMR IOW IOR DACK3 DRQ3 DACK1 DRQ1 DACK0 CLK IRQ7 IRQ6 IRQ5 IRQ4 IRQ3 DACK2 T C BALE 5V OSC GND GND U6 22V10 1 2 3 4 5 6 7 8 9 10 11 13 14 15 16 17 18 19 20 21 22 23 C...

Страница 75: ...IN5 IN6 IN7 IN8 A0 A1 A2 EN GND V V OUT R1 RESERVED U3 508A 4 5 6 7 12 11 10 9 1 16 15 2 14 3 13 8 IN1 IN2 IN3 IN4 IN5 IN6 IN7 IN8 A0 A1 A2 EN GND V V OUT J7 1 2 C14 1 1 2 R2 RESERVED C15 1 1 2 U2 INA...

Страница 76: ...WARRANTIES BY WINSYSTEMS EXCEPT AS STATED HEREIN THERE ARE NO OTHER WARRANTIES EXPRESS OR IMPLIED INCLUDING BUT NOT LIMITED TO THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR P...

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