MC68LC302 Datasheet, PDF (81/169 Pages) Motorola, Inc – Low Power Integrated Multiprotocol Processor Reference Manual

Communications Processor (CP)
and RBCS bits set, software operation mode, and the transmitter disabled. After a few
characters have been received, the transmitter can be enabled, and the software echo
function may be performed after issuing the RESTART TRANSMIT command.
In general, the autobaud controller uses the same data structure as that of the UART con-
troller. The first character (if matched) is stored in the receiver control character register and
the external data buffer, and the status of that character is reported in the autobaud com-
mand descriptor. After the first character, each incoming character is then stored in the
buffer pointed to by RxPTR, and the status is updated in the autobaud command autobaud
descriptor. The Tx internal data pointer (at offset SCC Base + 94) is updated to point to the
last character stored in the external data buffer.
4.3.9.4.2 Enter_Baud_Hunt Command. This command instructs the autobaud controller
to begin searching for the baud rate of a user predefined character. Prior to issuing the com-
mand the M68000 prepares the autobaud command descriptor to contain the lookup table
size and pointer.
The Enter_Baud_Hunt uses the GCI command with opcode = 10, and the channel number
set for the corresponding SCC. For example, with SCC1, the value written to the command
register would be $61.
4.3.9.4.3 Autobaud Command Descriptor. The autobaud controller uses the receive
buffer descriptor number 7 (Rx BD7) as an autobaud command descriptor. The autobaud
command descriptor is used by the M68000 core to transfer command parameters to the
autobaud controller, and by the autobaud controller to report information concerning the
received character.
The structure of the autobaud command descriptor for the autobaud process is shown in
Table 4-4. The first word of the descriptor or the status word is updated after every character
is received.
Table 4-4. Autobaud Command Descriptor
Offset 15 14 13 12 11 10 9 8 7 6 5
0
FE M2 M1
2
Lookup Table Size
4
Function Code
8
Lookup Table Pointer
4 3 21 0
EOT
OV CD
FE – Framing Error (Bit 10)
If this bit is set, a character with a framing error was received. A framing error is detected
by the autobaud controller when no STOP bit is detected in the received data. FE will be
set for a 9-bit character (8 bits + parity) if the parity bit is ‘0’.
NOTE
The user must clear this bit when it is set.
4-14
MC68LC302 REFERENCE MANUAL
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