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Z86E30/E31/E40
Zilog
Z8 4K OTP Microcontroller
DS97Z8X0502
P R E L I M I N A R Y
25
1
Port 0
(P07–P00). Port 0 is an 8-bit, bidirectional, CMOS-
compatible I/O port. These eight I/O lines can be config-
ured under software control as a nibble I/O port, or as an
address port for interfacing external memory. The input
buffers are Schmitt-triggered and nibble programmed. Ei-
ther nibble output that can be globally programmed as
push-pull or open-drain. Low EMI output buffers can be
globally programmed by the software. Port 0 can be placed
under handshake control. In Handshake Mode, Port 3
lines P32 and P35 are used as handshake control lines.
The handshake direction is determined by the configura-
tion (input or output) assigned to Port 0's upper nibble. The
lower nibble must have the same direction as the upper
nibble.
For external memory references, Port 0 provides address
bits A11–A8 (lower nibble) or A15–A8 (lower and upper
nibble) depending on the required address space. If the
address range requires 12 bits or less, the upper nibble of
Port 0 can be programmed independently as I/O while the
lower nibble is used for addressing. If one or both nibbles
are needed for I/O operation, they must be configured by
writing to the Port 0 mode register. In ROMless mode, after
a hardware reset, Port 0 is configured as address lines
A15–A8, and extended timing is set to accommodate slow
memory access. The initialization routine can include re-
configuration to eliminate this extended timing mode. In
ROM mode, Port 0 is defined as input after reset.
Port 0 can be set in the High-Impedance Mode if selected
as an address output state, along with Port 1 and the con-
trol signals AS, DS, and R/W (Figure 18).
Figure 18. Port 0 Configuration
Handshake Controls
/DAV0 and RDY0
(P32 and P35)
In
1.5 2.3V Hysteresis
PAD
Port 0 (I/O)
4
4
OEN
Out
Open-Drain
Auto Latch
R 500 k