Special Functions - ZiLOG Z8 Technical Manual

I/O Ports
Port 3 outputs cannot be written if they are used
for special functions. When writing to Port 3,
data is stored in the output register.
Table 9.1 Port J line Functions
Function line Signal
The port is read by specifying P3 as the source
register of an instruction. When reading from
Port 3, the data returned is both the data on the
input pins and in the output register.
Input
Output
P30-P33 Input
P34-P37 Output
9.5.2 Special Functions
Special functions for Port 3 are defined by pro-
gramming the Port 3 Mode register. By writing Os
in D2-D6' lines P30-P37 ar configured in input/
output pairs (Figure 9-14). Table 9-1 shows
available functions for Port 3.
The special
functions indicated in the table are discussed in
detail in their corresponding sections in this
manual.
Port 3 input lines P30-P33 always function as
interrupt requests regardless of the configuration
specified in the Port 3 Mode register. Unwanted
interrupts must be masked off as described in
Chapter 10.
R247 P3M
Port 3 Mode Register
(% F7; Write Only)
Handshake
Inputs
Handshake
Outputs
Interrupt
Requests
Serial Input
Output
Counter/Timer
Status
L . . . . .
='NPUT
P3s
=
OUTPUT
P3s
=
RDYO/DAVO
3047-012
1 P32
=
DAVO/RDYO
o 0 P33
=
INPUT
L -_ _ _ _
~ ~}P33
=
INPUT
1 1 P33
=
DAV1/RDY1
L-_ _ _ _ _ _ _
O P31
=
INPUT
(TIN)
1 P31
=
DAV2IRDY2
OP30
=
INPUT
L-_ _ _ _ _ _ _ _
1 P30
=
SERIAL IN
P34
=
OUTPUT
P34
=
DM
P34 = RDY1/DAV1
P36
=
OUTPUT
(TOUT)
P36
=
RDY2IDAV2
P3T
=
OUTPUT
P3T
=
SERIAL OUT
Figure 9-14. Port
J
I/O Operation
DAV 2 /RDY 2
DAVO/RDYO
DAV 1 /RDY 1
RDY 1 /DAV 1
RDYO/DAV O
RDY2/0AV2
51
SO
9-7