z89136 ZiLOG Semiconductor, z89136 Datasheet - Page 26

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

PIN FUCTIONS (Continued)
Z89135/136 (ROMless)
Low-Cost DTAD Controller
Port 4. (P47-P40). Port 4 is an 8-bit, bidirectional, CMOS-
compatible I/O port (Figure 14). These eight I/O lines are
configured under software control as an input or output, in-
dependently. Port 4 is always available for I/O operation.
The input buffers are Schmitt-triggered. Bits programmed
as outputs may be globally programmed as either push-
pull or open-drain.
1-26
Open-Drain
OEN
Out
In
1.5
Z89135/136
2.3V Hysteresis
Figure 14. Port 4 Configuraton
MCU
P R E L I M I N A R Y
R = 500 K
Port 4 is a bit programmable general-purpose I/O port. The
control registers for Port 4 are mapped into the expanded
register file (Bank F) of the Z8.
Auto Latch. The Auto Latch on Port 4 puts valid CMOS
levels on all CMOS inputs which are not externally driven.
Whether this level is 0 or 1, cannot be determined. A valid
CMOS level, rather than a floating node, reduces exces-
sive supply current flow in the input buffer.
Port 4
(I/O)
Auto Latch
PAD
DS97TAD0300
Zilog