Zilog Z80180 User Manual
Page 134
Z8018x
Family MPU User Manual
UM005003-0703
119
ASCI Receive Shift Register 0,1(RSR0, 1)
This register receives data shifted in on the RXA pin. When full, data is
automatically transferred to the ASCI Receive Data Register (RDR) if it
is empty. If RSR is not empty when the next incoming data byte is shifted
in, an overrun error occurs. The RSR is not program-accessible.
ASCI Receive Data Register 0,1 (RDR0, 1: I/O Address =
08H
,
09H
)
When a complete incoming data byte is assembled in RSR, it is
automatically transferred to the RDR if RDR is empty. The next incoming
data byte can be shifted into RSR while RDR contains the previous
received data byte. Thus, the ASCI receiver on Z80180 is double-
buffered.
\
On the Z8S180 and Z8L180-class processors are quadruple buffered. The
ASCI Receive Data Register is a read-only register. However, if RDRF =
ASCI Receive Data Register Ch. 0 (RDR0: 08H)
Bit
7
6
5
4
3
2
1
0
Bit/Field
ASCI Receive Channel 0
R/W
R/W
Reset
0
Note: R = Read W = Write X = Indeterminate ? = Not Applicable
ASCI Receive Data Register Ch. 1 (RDR1: 09H)
Bit
7
6
5
4
3
2
1
0
Bit/Field
ASCI Receive Channel 1
R/W
R/W
Reset
0
Note: R = Read W = Write X = Indeterminate ? = Not Applicable