
Serial Communications Interface Module (SCI)
General Release Specification
MC68HC(7)08LN56 — Rev. 2.0
234
Serial Communications Interface Module (SCI)
MOTOROLA
NONDISCLOSURE
AGREEMENT
REQUIRED
NOTE:
When DMATE = 1, a write by the CPU to the SCI data register can
inadvertently clear the SCTE bit and cause the DMA to miss a service
request.
NOTE:
Setting the TE bit for the first time also sets the SCTE bit. When enabling
SCI transmitter DMA service requests, set the TE bit after setting the
DMATE bit. Otherwise setting the TE and SCTIE bits generates an SCI
transmitter CPU interrupt request instead of a DMA service request.
TC — Transmission Complete Bit
This read-only bit is set when the SCTE bit is set, and no data,
preamble, or break character is being transmitted. TC generates an
SCI transmitter CPU interrupt request if the TCIE bit in SCC2 is also
set. When the DMA services an SCI transmitter DMA service request,
the DMA clears the TC bit by writing to the SCDR. TC is automatically
cleared when data, preamble or break is queued and ready to be sent.
There may be up to 1.5 transmitter clocks of latency between
queueing data, preamble, and break and the transmission actually
starting. Reset sets the TC bit.
1 = No transmission in progress
0 = Transmission in progress
SCRF — SCI Receiver Full Bit
This clearable, read-only bit is set when the data in the receive shift
register transfers to the SCI data register. SCRF can generate an SCI
receiver CPU interrupt request or an SCI receiver DMA service
request. When the SCRIE bit in SCC2 is set and the DMARE bit in
SCC3 is clear, SCRF generates a CPU interrupt request. With both
the SCRIE and DMARE bits set, SCRF generates a DMA service
request. In normal operation, clear the SCRF bit by reading SCS1
with SCRF set and then reading the SCDR. In DMA transfers, the
DMA clears the SCRF bit when it reads the SCDR. Reset clears
SCRF.
1 = Received data available in SCDR
0 = Data not available in SCDR
NOTE:
When DMARE = 1, a read by the CPU of the SCI data register can
inadvertently clear the SCRF bit and cause the DMA to miss a service
request.