Z89135 Datasheet, PDF (26/66 Pages) Zilog, Inc. – Low-Cost DTAD Controller

Z89135/136 (ROMless)
Low-Cost DTAD Controller
PIN FUCTIONS (Continued)
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.
Zilog
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.
Z89135/136
MCU
Port 4
(I/O)
Open-Drain
OEN
Out
1.5
2.3V Hysteresis
In
R = 500 KΩ
Figure 14. Port 4 Configuraton
PAD
Auto Latch
1-26
PRELIMINARY
DS97TAD0300