RCVDL56DPFL/SP, RCV56DPFL/SP, and RCV336DPFL/SP Designer’s Guide
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9-1
9. V.8 OPERATION CONSIDERATIONS
The host can access several registers in RAM to control and monitor V.8 operation (see Section 4). There are five control
registers (Table 9-1) and three status registers (Table 9-2). The host also has access to 13 registers which contain the
configuration (CONF) codes associated with the 13 modes of operation (Table 9-3).
To enter V.8 mode, load the interface memory CONF register (Table 3-1) with AA and then set the NEWC bit.
9.1 V.8 ORIGINATING MODEM OPERATING PROCEDURE
Once in the V.8 mode, set DTR to initiate the V.8 handshake.
In originate mode, the transmitter is set up to transmit Silence by default. (Optionally, CI may be sent if the host sets bit
304h:2.) The receiver is set up to detect ANS and ANSam. The data pump sets bit 301h:5 when ANS is detected and sets
bit 302h:3 when ANSam is detected.
9.1.1 Originating Without CI Option (Default)
Once ANSam is detected, the transmitter waits a silence period before transmitting CM. The silence period is 500 ms if no
phase reversals are detected in ANSam, otherwise the silence period is 1 second. The CM sequence consists of a
Preamble, followed by a SYNC octet, a Data Call Function Category octet, at least one modulation mode octet, an optional
protocol octet, and an optional GSTN octet (Table 9-4). The 16-byte transmit buffer, located at address 32Dh, is loaded with
the CM sequence once ANSam is detected.
The number of modulation mode octets transmitted is a function of the bit settings in control addresses 306h to 308h (Table
9-1). For example, if no modulation bits are set in addresses 307h or 308h, then only one modulation octet is sent (modn0).
On the other hand, if bits are set in address 307h, but not in address 308h, then modn0 and modn1 are sent. Only when
address 308h contains non-zero modulation bits will all three modulation octets be sent.
The protocol octet is transmitted if bit 305h:0 is set. The 3-bit protocol field is located in bits 305h:7-5. The default protocol
bits are set to indicate LAPM availability. The GSTN octet is sent if bit 304h:4 is set. The GSTN octet will be sent indicating
cellular access if bit 305h:2 is set.
CM transmission continues until JM is detected. When JM is detected, the current CM octet is completed and then CJ gets
appended to the transmitted data stream. A 75 ms silence period follows CJ transmission and the CONF register is updated
to the “Modulation Mode” indexed by the highest common modulation mode in JM (Table 9-3).
If no modulation modes are common, the CONF register changes to AFh, the “V.8 Cleardown” mode.
9.1.2 Originating With CI Option
Once DTR transitions on, the transmitter is silent for 400 ms before the CI sequence (Table 9-5) is transmitted. CI is sent
with a regular cadence of 1 second on and 1 second off. The on and off times are accessible via memory access (Section 4,
Functions 89). In particular, the on time counter, MaxFrameByteCount, is located at 31Ch. This counter is a “byte” counter
and defaults to 30 bytes for CI transmission. (Note that the MaxFrameByteCount should not be less than 9 { = 3 frames} if
the minimum three frames of CI is desired.) If this location is negative (i.e., MSB = 1), then there is no cadence applied to
the transmitted V.8 frame.
Note: MaxFrameByteCount = FFh when transmitting CM and JM.
The CI cadence will continue until ANSam is detected and the minimum three CI frames have been transmitted. Upon
detection of ANSam, CM is sent in the manner described in Section 9.1.1.
9.2 V.8 ANSWERING MODEM OPERATING PROCEDURE
If configured as the V.8 answer modem, the transmitter will transmit ANSam with VFC PN+ID (304h:3 = 0) or ANSam alone
(304h:3 = 1). The receiver will detect V.8 frames CI, CM, and CJ. Bits 301h:3-1 hold the status of CM, CI, and CJ detection
(Table 9-2).
When CM is detected, a JM frame is constructed using parameters from CM (Table 9-6).
The JM sequence starts with the 10 ONES preamble followed by the synchronization octet. Next comes the call function. If
the received CM octet contains the same call function as the answer modem’s “preferred” call function, then the same call
function that was received in CM is also sent in JM.
If the CM octet contains a different call function that the “preferred” call function, then the CallFunctionAllowed register
(address 32Ah) is consulted. (Table 9-7).The host can set up the CallFunctionAllowed register to indicate the call functions
that it allows. It is a bit-mapped register where bit k is set if call function 2k is to be allowed. If the call function received in
CM does not match any allowable call functions, then the preferred call function is returned with all modulation bits set to
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