Z86C21 Datasheet, PDF (9/35 Pages) Zilog, Inc. – 8K ROM Z8 CMOS MICROCONTROLLER

Port 2 (P27-P20). Port 2 is an 8-bit, bit programmable,
bidirectional, CMOS compatible port. Each of these eight
I/O lines can be independently programmed as an input or
output or globally as an open-drain output. Port 2 is always
available for I/O operation. When used as an I/O port,
Port 2 may be placed under handshake control. In this
Z86C21 MCU
WITH 8K ROM
configuration, Port 3 lines P31 and P36 are used as the
handshake control lines /DAV2 and RDY2. The handshake
signal assignment for Port 3 lines P31 and P36 is dictated
by the direction (input or output) assigned to P27
(Figure 7).
Z86C21
MCU
Open-Drain
OEN
Port 2 (I/O)
Handshake Controls
/DAV2 and RDY2
(P31 and P36)
PAD
Out
TTL Level Shifter
In
R ≈ 500 KΩ
Figure 7. Port 2 Configuration
Auto Latch
9