Z89175 Zilog., Z89175 Datasheet - Page 28

• Manufacturer Part Number: Z89175
• Description: Voice Processing Controllers
• Manufacturer: Zilog.

PIN FUNCTIONS (Continued)
Z89175/Z89176
Voice Processing Controllers
Port 4 (P47-P40). Port 4 is an 8-bit, bidirectional, CMOS
compatible I/O port (Figure 15). These eight I/O lines are
configured under software control independently as inputs
or outputs. Port 4 is always available for I/O operation. The
input buffers are Schmitt-triggered. Bits programmed as
outputs can be globally programmed as either push-pull or
open-drain.
28
Open-Drain
OEN
Out
In
1.5
Z89175/176
2.3V Hysteresis
Figure 15. Port 4 Configuration
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
DS97TAD0100
Pad
Zilog