Z86L7208FSC datasheet(33/71 Pages) ZILOG

33 / 71 page

Z86C72/C92/L72/L92

Zilog

IR Microcontroller

DS97LVO0900

P R E L I M I N A R Y

6-33

port registers, 236 general-purpose registers, and 16 con-

trol and status registers (R0-R3, R4-R239, and R240-

R255, respectively), Plus two expanded registers groups

(Banks D and F). Instructions can access registers directly

or indirectly through an 8-bit address field. This allows a

short, 4-bit register address using the Register Pointer

(Figure 23). In the 4-bit mode, the register file is divided

into 16 working register groups, each occupying 16 contin-

uous locations. The Register Pointer addresses the start-

ing location of the active working register group.

Note: Working register group E0-EF can only be access-

ed through working registers and indirect addressing

modes.

Stack. The Z86L/CX2 external data memory or the inter-

nal register file is used for the stack. An 8-bit Stack Pointer

(R255) is used for the internal stack that resides in the gen-

eral-purpose registers (R4-R239). SPH is used as a gen-

eral-purpose register only when using internal stacks.

Note: When SPH is used as a general-purpose register

and Port 0 is in address mode, the contents of SPH will be

loaded into Port 0 whenever the internal stack is accessed.

Figure 20. Register Pointer

Expanded Register File Pointer

Working Register Pointer

R253 RP

Default Setting After Reset = 0000 0000

Figure 21. Register Pointer

The upper nibble of the register file address

provided by the register pointer specifies

the active working-register group

R253

I/O Ports

Specified Working

The lower nibble

of the register

file address

provided by the

instruction points

to the specified

R15 to R4

R3 to R0

R15 to R0

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