MC908GR32AVFAE Datasheet, PDF (171/314 Pages) Freescale Semiconductor, Inc – Microcontrollers

I/O Registers
SCTE — ESCI Transmitter Empty Bit
This clearable, read-only bit is set when the SCDR transfers a character to the transmit shift register.
SCTE can generate an ESCI transmitter CPU interrupt request. When the SCTIE bit in SCC2 is set,
SCTE generates an ESCI transmitter CPU interrupt request. In normal operation, clear the SCTE bit
by reading SCS1 with SCTE set and then writing to SCDR. Reset sets the SCTE bit.
1 = SCDR data transferred to transmit shift register
0 = SCDR data not transferred to transmit shift register
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 ESCI transmitter CPU interrupt request if the TCIE bit in SCC2 is also
set. TC is cleared automatically 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 — ESCI Receiver Full Bit
This clearable, read-only bit is set when the data in the receive shift register transfers to the ESCI data
register. SCRF can generate an ESCI receiver CPU interrupt request. When the SCRIE bit in SCC2 is
set the SCRF generates a CPU interrupt request. In normal operation, clear the SCRF bit by reading
SCS1 with SCRF set and then reading the SCDR. Reset clears SCRF.
1 = Received data available in SCDR
0 = Data not available in SCDR
IDLE — Receiver Idle Bit
This clearable, read-only bit is set when 10 or 11 consecutive 1s appear on the receiver input. IDLE
generates an ESCI receiver CPU interrupt request if the ILIE bit in SCC2 is also set. Clear the IDLE
bit by reading SCS1 with IDLE set and then reading the SCDR. After the receiver is enabled, it must
receive a valid character that sets the SCRF bit before an idle condition can set the IDLE bit. Also, after
the IDLE bit has been cleared, a valid character must again set the SCRF bit before an idle condition
can set the IDLE bit. Reset clears the IDLE bit.
1 = Receiver input idle
0 = Receiver input active (or idle since the IDLE bit was cleared)
OR — Receiver Overrun Bit
This clearable, read-only bit is set when software fails to read the SCDR before the receive shift
register receives the next character. The OR bit generates an ESCI error CPU interrupt request if the
ORIE bit in SCC3 is also set. The data in the shift register is lost, but the data already in the SCDR is
not affected. Clear the OR bit by reading SCS1 with OR set and then reading the SCDR. Reset clears
the OR bit.
1 = Receive shift register full and SCRF = 1
0 = No receiver overrun
Software latency may allow an overrun to occur between reads of SCS1 and SCDR in the flag-clearing
sequence. Figure 13-14 shows the normal flag-clearing sequence and an example of an overrun
caused by a delayed flag-clearing sequence. The delayed read of SCDR does not clear the OR bit
because OR was not set when SCS1 was read. Byte 2 caused the overrun and is lost. The next
flag-clearing sequence reads byte 3 in the SCDR instead of byte 2.
MC68HC908GR60A • MC68HC908GR48A • MC68HC908GR32A Data Sheet, Rev. 5
Freescale Semiconductor
171