z89138 ZiLOG Semiconductor, z89138 Datasheet - Page 31

• Manufacturer Part Number: z89138
• Description: Voice Processing Controllers
• Manufacturer: ZiLOG Semiconductor

Zilog
Register File. The standard Z8 register file consists of 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 registers di-
rectly or indirectly through an 8-bit address field. This al-
lows a short, 4-bit register address using the Register
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 (Fig-
ure 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
register address space has been implemented as 16
banks of 16 register 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 21).
DS97TAD0201
P R E L I M I N A R Y
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.
R253 RP
D7 D6 D5 D4
Figure 19. Register Pointer Register
Group 15 (F) Control Registers
The upper nibble of the register file address
provided by the register pointer specifies
the active working-register group
Group 14 (E)
Group 13 (D)
Group 4 (4)
Group 3 (3)
Group 2 (2)
Group 1 (1)
Group 0 (0)
r7 r6 r5 r4
Figure 20. Register Pointer
D3 D2 D1 D0
I/O Ports
Specified Working
Register Group
r3 r2 r1 r0
Voice Processing Controllers
Expanded Register File Bank
Working Register Group
R255
R253
R240
R15
R239
R223
R79
R63
R47
R31
R3
R0
Z89138/Z89139
The upper nibble
of the register
file address
provided by the
instruction points
to the specified
working-register
group
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