Z8 Microcontrollers
External Interface
ZiLOG
10-2
UM001600-Z8X0599
10.2 PIN DESCRIPTIONS
The following sections briefly describe the pins associated
with the Z8 MCU
external memory interface.
10.2.1 /AS
Address Strobe (output, active Low). Address Strobe is
pulsed Low once at the beginning of each machine cycle.
The rising edge of
AS
indicates the address, Read/Write
(R/
W
), and Data Memory (
DM
) signals are valid for pro-
gram or data memory transfers. In some cases, the Z8 ad-
dress strobe is pulsed low regardless of accessing exter-
nal or internal memory. Please refer to specific product
specifications for
AS
operation.
10.2.2
DS
Data Strobe (Output, Active Low). Data Strobe provides
the timing for data movement to or from the Address/Data
bus for each external memory transfer. During a Write Cy-
cle, data out is valid at the leading edge of the
DS
. During
a Read Cycle, data in must be valid prior to the trailing
edge of the
DS
.
10.2.3 R/
W
Read/Write (Output). Read/Write determines the direction
of data transfer for memory transactions. R/
W
is Low when
writing to program or data memory, and High for all other
transactions.
10.2.4 DM
Data Memory (Output).Data Memory provides a signal to
separate External Program Memory from External Data
Memory. It is a programmable function on pin P34. Data
memory is active low for External Data Memory accesses
and high for External Program Memory accesses.
10.2.5 P07 - P00
High Address LinesA15 -A8 (Outputs can be CMOS- or
TTL- compatible. Please refer to product specifications for
actual type). A15-A8 provide the High Address lines for the
memory interface. Port 0 - 1 mode register must have bits
D7 = 1 and D1 = 1 to configure Port 0 as A15 - A8 (Figure
10-2).
10.2.6 P17 - P10
Address/Data LinesAD7 - AD0 (inputs/outputs, TTL-com-
patible). AD7-AD0 is a multiplexed Address/Data memory
interface. The lower eight Address lines (A7-A0) are multi-
plexed with Data lines (D7-D0). Port 0 - 1 mode register
must have bits D4 = 1 and D3 = 0 to configure Port 1 as
AD7 - AD0 (Figure 10-2).
10.2.7 /RESET
Reset(input, active Low).
RESET
initializes the Z8. When
RESET
is deactivated, program execution begins from
program location 000CH. If held Low,
RESET
acts as a
register file protect during power-down and power-up
sequences. To avoid asynchronous and noisy reset
problems, the Z8 is equipped with a reset filter of four
external clocks (4T
P
C). If the external
RESET
signal is less
than 4T
P
C in duration, no reset will occur. On the fifth clock
after the
RESET
is detected, an internal reset signal is
latched and held for an internal register count of 18 or
more external clocks, or for the duration of the external
RESET
, whichever is longer. Please refer to specific
product specifications for length of reset delay time.
10.2.8 XTAL1, XTAL2.
Crystal1, Crystal2 Oscillator input and output). These pins
connect a parallel-resonant crystal, ceramic resonator, LC,
RC network, or external single-phase clock to the on-chip
oscillator input. Please refer to the device product specifi-
cations for information on availability of RC oscillator fea-
tures.