Serial Communication Controllers (SCCs)
MC68360 USER’S MANUAL
DRT—Disable Receiver While Transmitting
0 = Normal operation
1 = While data is being transmitted by the SCC, the receiver is disabled, being gated
by the internal RTS signal. This configuration is useful if the HDLC channel is con-
figured onto a multidrop line and the user does not wish to receive his own trans-
mission.
BUS—HDLC Bus Mode
0 = Normal HDLC operation
1 = HDLC Bus operation selected. See 7.10.18 HDLC Bus Controller for more details.
BRM—HDLC Bus RTS Mode
This bit is only valid if BUS = 1; otherwise, it is ignored.
0 = Normal RTS operation during HDLC Bus mode. RTS is asserted on the first bit of
the transmit frame and negated after the first collision bit is received.
1 = Special RTS operation during HDLC Bus mode. RTS is delayed by one bit with re-
spect to the normal case. This is useful when the HDLC Bus protocol is run locally,
and at the same time, transmitted over a long-distance transmission line. Data may
be delayed by one bit before it is sent over the transmission line; thus, RTS may
be used to enable the transmission line buffers. The result is a clean signal level
sent over the transmission line.
MFF—Multiple Frames in FIFO
0 = Normal operation. The transmit FIFO can never contain more than one HDLC
frame. The CTS lost status will be reported accurately on a per-frame basis. The
receiver is not affected by this bit.
1 = The transmit FIFO can contain multiple frames, but CTS lost is not guaranteed to
be reported on the exact buffer/frame on which it truly occurred. This option, how-
ever, can improve the performance of HDLC transmissions in cases of small back-
to-back frames or in cases where the user desires to strongly limit the number of
flags transmitted between frames. The receiver is not affected by this bit.
7.10.17.9 HDLC RECEIVE BUFFER DESCRIPTOR (RX BD). The HDLC controller uses
the Rx BD to report information about the received data for each buffer. An example of the
Rx BD process is shown in Figure 7-52.
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Freescale Semiconductor, Inc.
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