Table 3·7. Set Value Opcodes
3.8 MODEM CONTROL
Two commands are provided to allow the TBC to communicate management services to the physical layer of the network.
3.8.1 PHYSICAL Command
This command is used by the host processor to control the modem while in station management and should only be given when the TBC is in the OFFLINE state. Status is returned to the last word in the command parameter area (CPA RESULT) as shown following the command format.
The physical data request channel is fully described in 5.9.1 Physical Data Request Channel while the physical data indication channel is described in 5.9.2 Physical Data Indication Channel. Note that SMREQ equals zero is an indication that station management has been selected. This signal is automatically asserted when the first physical command is issued by the host. SMREQ will stay low until the END PHYSICAL command (see 3.8.2 END PHYSICAL Command) is issued by the host to terminate station management. SMREQ is also referred as TXSYM3 in the 802.4G docu-ment.
The coding for the physical command is A1-A7 and its format is shown below:
2 1 0
o I
DATAI
TXSYM2I
TXSYMlMC68824 USER'S MANUAL MOTOROLA
II
II
TXSYM2
1 TXSYM2 line to the modem is set to one while SMREO equals zero
o
TXSYM2 line to the modem is set to zero while SMREO equals zero TXSYM11 TXSYM1 line to the modem is set to one while SMREO equals zero
o
TXSYM1 line to the modem is set to zero while SMREO equals zero DATA1 Perform data exchange with the modem
o
No data exchangeNote that the PHYSICAL command should not be given with a code of AO as this commands the modem to enter the idle state without a data transfer. This action would then cause the modem to respond with idle whereas the TBC would be waiting for ACK or NACK. Only the TBC is permitted to issue idle to the modem without a data transfer.
The status word format returned in CPA RESULT is shown below:
x x x
RXACK - RXSYM1 Acknowledgement 1 Acknowledgement received
o
No acknowledgement received RXNA - RXSYM2 Non-Acknowledgement1 Non-acknowledged received
o
No non-acknowledgement received COMCON - Command Configuration1 Command confirmed
o
Command not confirmedx -
Don't Carex x
RXACK RXNAI
COMCONThere are two main types of commands which can be issued by the host to the physical layer:
immediate and data transfer. Immediate commands do not involve data exchange with the modem but rather provide a simple interface to allow the host to control the modem through the TBC.
Data transfer commands are designed for intelligent modems which need additional information to be transferred between the host and the modem through the TBC.
3.S.1.1 IMMEDIATE COMMANDS. The immediate commands include reset, disable loopback,and enable transmitter. Refer to 5.9. ;.4 TXSYM2, TXSYM1, AND TXYSMO IN STATION MANAGEMENT MODE for a description of the encodings of these commands on the physical interface. The following paragraphs describe the handshake between the TBC and the modem. The host loads the command into the command register and the TBC passes the command to the modem by encoding it on pins TXSYM1 and TXSYM2 while TXSYMO is set to one. Note that for immediate commands, bit 2 (DATA) of the command register must be set to zero. Upon receiving this type of command the TBC will go through the steps described below:
1. It is assumed that the TBC and the modem are in MAC mode or that a modem error just occurred.
MOTOROLA MC68824 USER'S MANUAL
'l~,)O
2. The TBC encodes the command found in CR on TXSYM1 and TXSYM2 with TXSYMO= 1 and SMREO equal to zero.
3. The TBC waits indefinitely for ACK or NACK coding on RXSYM1 and RXSYM2 as well as SMIND=O from the modem.
NOTES
The modem is free to go to idle before transitioning to this state. If the modem does not respond after a reasonable length of time, a software or hardware RESET must be
issued to the TBC.
II
4. The TBC samples the ACKINACK signals (RXSYM1 and RXSYM2) and issues idle to the modem (TXSYM2=0, TXSYM1 =0, while TXSYMO=1, and SMREO=O).
5. The TBC waits for the modem to respond with idle (RXSYM2=0, RXSYM1 =0, while SMIND=O).
NOTE
If the modem does not respond after a reasonable length of time, a software or hardware RESET must be issued to the TBC.
6. The TBC updates the CPA result with the ACKINACK and command done bits.
7. At this point, the TBC is in SM idle mode with TXSYM2=0, TXSYM1 =0, TXSYMO= 1, and SMREO=O. The modem is in the idle state with RXSYM2=0, RXSYM1 =0, and SMIND=O.
S. The TBC is ready to accept another command.
3.8.1.2 DATA TRANSFER COMMANDS. Data transfer commands are designed for intelligent mo-dems which need more information. The serial station management data interface provides a sophisticated way for the host to communicate with the modem through the TBC. Upon receiving this type of command the TBC will go through the steps described below:
1. It is assumed that the TBC and the modem are in MAC mode or that a modem error just occurred.
2. The TBC issues the data transfer command found in CR with TXSYMO=1 and SMREO=O to the mO,dem.
3. The TBC waits indefinitely for the modem to assert SMIND = O.
NOTE
If the modem does not respond after a reasonable length of time, a software or hardware RESET must be issued to the TBC.
4. The TBC samples RXSYM 1 and RXSYM2 for ACKINACK from now to the end of the received data stream.
5. The TBC outputs the bit stream taken from CPA VALO (16 bits from 0 to 15) on TXSYMO.
The data word in CPA VALO must include the start bit as shown to conform to S02.4G:
CPA VALO: D C B A 4
Data Start Bit
NOTE
The programmer does not have to furnish the stop bit.
To conform to S02.4G only one data byte may be sent at a time. If more than one data byte needs to be sent, then more data commands must be given.
MC68824 USER'S MANUAL MOTOROLA
,)_,)0
II
6. The TBC waits indefinitely for the modem to assert the start bit i.e., RXSYMO = O.
NOTE
Ifthe modem does not respond after a reasonable length oftime, a software or hardware RESET must be issued to the TBC. .
7. The TBC waits 16 clock cycles to sample the 16 bits after the start bit from RXSYMO.
S. The TBC asserts TXSYMO = 1, TXSYM 1 = 0, TXSYM2 = 0 with SMREQ = 0, thus issuing idle.
9. The TBC waits for the modem to respond with idle: RXSYM1 =0, RXSYM2=0, while SMIND=O.
10. The TBC then copies the received word into CPA RET O. Bits 0 through 7 contain the data returned by the modem while bits S through F contain all ones if the S02.4G interface was used.
11. The TBC updates the CPA result with the ACKINACK and command done bits.
12. At this point, the TBC is in SM idle mode with TXSYM2=0, TXSYM1 =0, TXSYMO= 1, and SMREQ=O. The modem is in the idle state with RXSYM2=0, RXSYM1 =0, and SMIND=O.
13. The TBC is ready to accept another command.
3.S.2 END PHYSICAL Command
This command causes the TBC to exit from station management mode. Upon receiving the command, the TBC sets SMREQ=1, and waits for the modem to set SMIND=1 before setting the command done bit (bit 0 of CPA RESULT). The coding for this command is AS and its format is: