Scc Transparent Mode Support - Motorola MC68302 User Manual

4.5.9 SCC Transparent Mode Support
The SCC supports several transparent receive and transmit modes, which
vary according to the protocol being implemented. As used here, transparent
means data transparency and is not the same as the promiscuous mode
described later in this section. The transparent modes for each protocol are
as follows:
UART Mode
If the nonautomatic mode is selected (AUTO= 0 in the UART mode register)
and the control characters table is empty, then the UART will transfer all
received characters to memory.
HOLC Mode
When HMASK=$0000, the HOLC controller will transfer all the received
frame to the receive buffers, including address, control, data, and CRC. The
HOLC controller still performs the standard HOLC functions of zero inser-
tion/deletion and flag recognition. For complete bit transparency, use the
promiscuous mode.
BISYNC Mode
The BISYNC mode may be used to transparently receive data that is de-
limited by SYNCs. To do this, the BISYNC control characters table should
be empty, and SYNC/OLE stripping should be disabled. Thereafter, all data
following the SYNCs will be received into the receive buffers.
There are two possible ways of recognizing SYNCs. Either the EXSYN bit
in the BISYNC mode register is cleared and a SYNC is defined by the
SYN1-SYN2 characters in DSR, or the EXSYN bit is set and a SYNC is
determined by an external SYNC pulse.
When the BISYNC control characters table is empty, the SYNC and OLE
stripping is disabled, and the BISYNC controller is in normal nontranspar-
ent mode (RTR
=
0 in BISYNC mode register). In this case, the configuration
is as follows:
If EXSYN in the BISYNC mode register is cleared, then the BISYNC con-
troller transfers all characters that follow the SYN1-SYN2 sequence to
the receive buffers.
If EXSYN in the BISYNC mode register is set, then the BISYNC controller
transfers all characters that follow the external SYNC pulse to the receive
buffers. This configuration is also used for promiscuous mode.
NOTE
The BISYNC controller can reverse the bit order in both modes.
MOTOROLA
MC68302 USER'S MANUAL 4-31