z89136 ZiLOG Semiconductor, z89136 Datasheet - Page 22

• Manufacturer Part Number: z89136
• Description: Low-cost Dtad Controller
• Manufacturer: ZiLOG Semiconductor

PIN FUCTIONS (Continued)
Z89135/136 (ROMless)
Low-Cost DTAD Controller
Port 1. (P17-P10). Port 1 is an 8-bit, bidirectional, CMOS-
compatible port (Figure11). It has multiplexed Address
(A7-A0) and Data (D7-D0) ports. These eight I/O lines are
programmed as inputs or outputs, or can be configured un-
der software control as an Address/Data port for interfac-
ing external memory. The input buffers are Schmitt trig-
gered and the output drivers are push-pull.
Port 1 may be placed under handshake control. In this con-
figuration, Port 3, lines P33 and P34 are used as the hand-
shake controls RDY1 and /DAV1 (Ready and Data Avail-
able). Memory locations greater than 24575 (in ROM
1-22
OEN
Out
In
1.5
Z89135/136
MCU
Figure 11. Port 1 Configuration
2.3V Hysteresis
P R E L I M I N A R Y
R = 500 K
8
mode) are referenced through Port 1. To interface external
memory, Port 1 must be programmed for the multiplexed
Address/Data mode. If more than 256 external locations
are required, Port 0 outputs the additional lines.
Port 1 can be placed in the high-impedance state along
with Port 0, /AS, /DS and R//W, allowing the Z89135/136
to share common resources in multiprocessor and DMA
applications.
Port 1
(I/O or AD7 - AD0)
Handshake Controls
/DAV2 and RDY2
(P31 and P36)
Auto Latch
PAD
DS97TAD0300
Zilog