z89136 ZiLOG Semiconductor, z89136 Datasheet - Page 31

• Manufacturer Part Number: z89136
• Description: Low-cost Dtad Controller
• Manufacturer: ZiLOG Semiconductor

Zilog
RAM Protect. The upper portion of the Z8’s RAM address
spaces 80FH to EFH (excluding the control registers) are
protected from reading and writing. The RAM Protect bit
option is mask-programmable and is selected by the cus-
tomer when the ROM code is submitted. After the mask
option is selected, the user activates from the internal
ROM code to turn off/on the RAM Protect by loading a bit
D6 in the IMR register to either a 0 or a 1, respectively. A
1 in D6 indicates RAM Protect enabled.
Stack. The Z8’s external data memory or the internal reg-
ister file is used for the stack. The 16-bit Stack Pointer
(R255-R254) is used for the external stack which can re-
side only from 24576 to 65535 in ROM Mode or 0 to 65535
in ROMless mode. An 8-bit Stack Pointer (R255) is used
for the internal stack that resides within the 236 general-
purpose registers (R239-R4). SPH can be used as a gen-
eral-purpose register when using internal stack only.
DS97TAD0300
P R E L I M I N A R Y
Expanded Register File. The register file on the Z8 has
been expanded to allow for additional system control reg-
isters, and for mapping of additional peripheral devices
along with I/O ports into the register address area. The Z8
register address space has now been implemented as 16
banks of 16 registers groups per bank (Figure 20). These
register banks are known as the ERF (Expanded Register
File). Bits 7-4 of register RP (Register Pointer) select the
working register group. Bits 3-0 of register RP select the
expanded register bank (Figure 20).
The SMR register, WDT register, control and data regis-
ters for Port 4 and Port 5, and the DSP control register are
located in Bank F of the Expanded Register File. Bank B
of the Expanded Register File consists of the Mailbox In-
terface in which the Z8 and the DSP communicate. The
rest of the Expanded Register is not physically implement-
ed and is open for future expansion.
Low-Cost DTAD Controller
Z89135/136 (ROMless)
1-31
1