Z89176 datasheet(32/68 Pages) ZILOG

32 / 68 page

Z89175/Z89176

Voice Processing Controllers

Zilog

P R E L I M I N A R Y

DS97TAD0100

Z8® FUNCTIONAL DESCRIPTION (Continued)

four I/O port registers, 236 general-purpose registers, and

15 control and status registers (R0-R3, R4-R239, and

R241-R255, respectively). The instructions access regis-

ters directly or indirectly through an 8-bit address field.

This allows a short, 4-bit register address using the Regis-

ter Pointer (Figure 19). In the 4-bit mode, the register file

is divided into 16 working register groups, each occupying

16 continuous locations. The Register Pointer addresses

the starting location of the active working register group

(Figure 20).

Note: Register Group E (Registers EF-E0) is only access-

ed through a working register and indirect addressing

modes.

RAM Protect. The upper portion of the Z8’s RAM address

spaces 80H to EFH (excluding the control registers) is pro-

tected from reading and writing. The RAM Protect bit op-

tion is mask-programmable and is selected by the custom-

er when the ROM code is submitted. After the mask option

is selected, the user activates the RAM Protect from the in-

ternal ROM code by loading a bit D6 in the IMR register to

either a 0 (OFF) or a 1 (ON). A 1 in D6 indicates RAM Pro-

tect 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 residing within the 236 general-pur-

pose registers (R239-R4). SPH can be used as a general-

purpose register when using internal stack only.

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

banks of 16 register groups per bank (Figure 20). These

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 21).

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 through which the Z8 and the DSP communicate.

The rest of the Expanded Register is not physically imple-

mented and is open for future expansion.

Figure 19. Register Pointer Register

D7 D6

R253 RP

Expanded Register File Bank

Working Register Group

Z89176 Datasheet(PDF) 32 Page - Zilog, Inc.

Z89176 Datasheet(HTML) 32 Page - Zilog, Inc.

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