Z86C21 datasheet(8/35 Pages) ZILOG

8 / 35 page

Z86C21 MCU

WITH

8K ROM

PIN FUNCTIONS (Continued)

Port 1 (P17-P10). Port 1 is an 8-bit, byte programmable,

bidirectional, TTL compatible port. It has multiplexed Ad-

dress (A7-A0) and Data (D7-D0) ports. For Z86C21, these

eight I/O lines can be programmed as Input or Output lines

or can be configured under software control as an ad-

dress/data port for interfacing external memory. When

used as an I/O port, Port 1 can be placed under handshake

control. In this configuration, Port 3 line P33 and P34 are

used as the handshake controls RDY1 and /DAV1.

Memory locations greater than 8192 are referenced through

Port 1. To interface external memory, Port 1 is programmed

for the multiplexed Address/Data mode. If more than 256

external locations are required, Port 0 must output the

additional lines.

Port 1 can be placed in a high-impedance state along with

Port 0, /AS, /DS and R//W, allowing the MCU to share

common resource in multiprocessor and DMA applica-

tions. Data transfers are controlled by assigning P33 as a

Bus Acknowledge input, and P34 as a Bus request output

(Figure 6).

OEN

Out

PAD

Port 1

(AD7-AD0)

Z86C21

MCU

TTL Level Shifter

Auto Latch

≈ 500 KΩ

Handshake Controls

/DAV1 and RDY1

(P33 and P34)

Figure 6. Port 1 Configuration

Z86C21 датащи(PDF) 8 Page - Zilog, Inc.