Z89135 Datasheet, PDF (31/66 Pages) Zilog, Inc. – Low-Cost DTAD Controller

Zilog
Z89135/136 (ROMless)
Low-Cost DTAD Controller
RAM Protect. The upper portion of the Z8’s RAM address Expanded Register File. The register file on the Z8 has
spaces 80FH to EFH (excluding the control registers) are been expanded to allow for additional system control reg-
1 ^{protected from reading and writing. The RAM Protect bit isters, and for mapping of additional peripheral devices}
option is mask-programmable and is selected by the cus- along with I/O ports into the register address area. The Z8
tomer when the ROM code is submitted. After the mask register address space has now been implemented as 16
option is selected, the user activates from the internal banks of 16 registers groups per bank (Figure 20). These
ROM code to turn off/on the RAM Protect by loading a bit register banks are known as the ERF (Expanded Register
D6 in the IMR register to either a 0 or a 1, respectively. A File). Bits 7-4 of register RP (Register Pointer) select the
1 in D6 indicates RAM Protect enabled.
working register group. Bits 3-0 of register RP select the
expanded register bank (Figure 20).
Stack. The Z8’s external data memory or the internal reg-
ister file is used for the stack. The 16-bit Stack Pointer The SMR register, WDT register, control and data regis-
(R255-R254) is used for the external stack which can re- ters for Port 4 and Port 5, and the DSP control register are
side only from 24576 to 65535 in ROM Mode or 0 to 65535 located in Bank F of the Expanded Register File. Bank B
in ROMless mode. An 8-bit Stack Pointer (R255) is used of the Expanded Register File consists of the Mailbox In-
for the internal stack that resides within the 236 general- terface in which the Z8 and the DSP communicate. The
purpose registers (R239-R4). SPH can be used as a gen- rest of the Expanded Register is not physically implement-
eral-purpose register when using internal stack only.
ed and is open for future expansion.
DS97TAD0300
PRELIMINARY
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