ZiLOG Z8 Technical Manual

I/O Ports
9.' PORT 1
This section deals only with the I/O operation of
Port 1 and does not apply to the Z8681/82 ROMless
devices. Refer to Sections 6.2 and 7.2 for a
description of the port's external memory inter-
face operation.
Port 1 is a general-purpose I/O port that can be
programmed as a byte I/O port with or without
handshake, or
as an address/data port for inter-
facing with external memory. Refer to Figure 9-2
for a block diagram of Port 1.
9.'.1 Read/Write Operations
In byte input or byte output mode, the port is
accessed as general-purpose register P1 (%01).
The port is written by specifying P1 as an
instruction's destination register. Writing the
port causes data to be stored in the port's output
register.
The port is read by specifying P1 as the source
register of an instruction. When an output is
read, data on the external pins is returned.
Under normal loading conditions, this is equiva-
lent to reading the output register. When Port 1
is defined as an input, reading also returns data
on the external pins. However, inputs under hand-
shake control return data latched into the input
register via the input strobe.
Using the Port 0-1 Mode register, Port 1 is con-
figured as an output port by setting bits 04 and
0
3
to Os, or as an input port by setting 04 to 0
and 03 to 1 (Figure 9-6).
R248 P01M
Port 0-1 Mode Register
(% F8; Write Only)
9-4
P1
o
-P1
7
MODE
00
= BYTE OUTPUT
01 = BYTE INPUT
10
= ADo-AD7
11 = HIGH·IMPEDANCE ADo-AD7,
AS, Os, RtW, Aa-A11. A12-A15
figure 9-6. Port 1 I/O Operation
9.'.2 Handshake Operations
When used as an I/O port, Port 1 can be placed
under handshake
control by programming the Port 3
Mode register bits 04 and 0
3
both to 1 (Figure
9-7). In this configuration, handshake control
lines are OAV
1
(P3
3
)
and RDY
1
(P3
4
)
when Port 1 is
an input port, or ROY1 (P3
3
)
and OAV
1
(P34)
when
Port 1 is an output port.
R247 P3M
Port 3 Mode Register
(% F7; Write Only)
o 0 P33 = INPUT
o 1 P33 = INPUT
1 0 P33 = INPUT
1 1 P33 = DAVi/RDY1
P34 = OUTPUT
P34 = OM
P34 = OM
P34 = RDY1/DAV1
Figure 9-7. Port 1 Handshake Operation
Handshake direction is determined by the configu-
ration (input or output) assigned to Port 1. For
example,
if Port 1 is an output port then hand-
shake is defined as output. Figure 9-8 illus-
trates the Port 1 lines and the associated hand-
shake
lines of Port 3.
Handshake operation is discussed in detail in Sec-
tion 9.6.
PORT 1
(1/0 OR ADo-AD7) P1o-P17
}
HANDSHAKE CONTROLS
DAV1 AND RDY1
(P3
3
AND P3~
Figure 9-8. Port 1
3047-004,3047-003,2037-008

ZiLOG Z8 Specifications

General

Brand	ZiLOG
Model	Z8
Category	Desktop
Language	English