Z8 Microcontrollers
Address Space
ZiLOG
UM001600-Z8X0599
2-11
2.6 Z8 EXTERNAL MEMORY
The Z8, in some cases, has the capability to access exter-
nal program memory with the 16-bit Program Counter. To
access external program memory the Z8 offers multi-
plexed address/data lines (AD7-AD0) on Port 1 and ad-
dress lines (A15-A8) on Port 0. This feature only applies to
devices that offer Port 0 and Port 1. The maximum external
address is FFFF. This memory interface is supported by
the control lines
AS
(Address Strobe),
DS
(Data Strobe),
and R/W (Read/Write). The origin of the external program
memory starts after the last address of the internal ROM.
Figure 2-8 shows an example of external program memory
for the Z8.
2.6.1 External Data Memory (/DM)
The Z8, in some cases, can address up to 60 Kbytes of ex-
ternal data memory beginning at location 4096. External
Data Memory may be included with, or separated from, the
external Program Memory space.
DM
, an optional I/O
function that can be programmed to appear on pin P34, is
used to distinguish between data and program memory
space. The state of the
DM
signal is controlled by the type
of instruction being executed. An LDC opcode references
Program (
DM
inactive) Memory, and an LDE instruction
references Data (
DM
active Low) Memory. The user must
configure Port 3 Mode Register (P3M) bits D3 and D4 for
this mode.
Note:
For additional information on using external memory, see Chapter 10 of this manual. For exact memory addressing options
available, see the device product specification.
Figure 2-8. External Memory Map
External
Memory
65535
4096
4095
Not Addressable
0