Z89135 Datasheet, PDF (29/66 Pages) Zilog, Inc. – Low-Cost DTAD Controller

Zilog
ROM Protect. The 24 KB of internal program memory for
the Z8 is mask programmable. A ROM protect feature pre-
vents “dumping” of the ROM contents of Program Memory
by inhibiting execution of LDC, LDCI, LDE, and LDEI in-
structions. The ROM Protect option is mask-programma-
ble, to be selected by the customer at the time when the
ROM code is submitted.
Data Memory. (/DM). In ROM Mode, the Z8 can address
up to 40 KB of external data memory beginning at location
24576 (Figure 17). In ROMless mode, the Z8 can address
the full 64 KB of external data memory beginning at loca-
tion 12. 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 Port 34, 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) mem-
ory, and an LDE instruction references data (/DM active
Low) memory.
65535
Z89135/136 (ROMless)
Low-Cost DTAD Controller
1
External
Data
Memory
24756
Not Addressable
(In ROM Mode)
0
Figure 17. Data Memory Map
DS97TAD0300
PRELIMINARY
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