Z89175 Zilog., Z89175 Datasheet - Page 31

• Manufacturer Part Number: Z89175
• Description: Voice Processing Controllers
• Manufacturer: Zilog.

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 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 18). In ROMless mode, the Z8 can address
the full 64 KB of external data memory beginning at loca-
tion 12. External data memory can 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 (Table 5). The state of the /DM
signal is controlled by the type of instruction being execut-
ed. An LDC opcode references PROGRAM (/DM inactive)
DS97TAD0100
P R E L I M I N A R Y
memory, and an LDE instruction references data (/DM ac-
tive Low) memory.
24575
65535
0
Figure 18. Data Memory Map
Not Addressable
(In ROM Mode)
Voice Processing Controllers
External
Memory
Data
Z89175/Z89176
31
2