Z86L78 datasheet(21/59 Pages) ZILOG

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Z86L78

Zilog

IR/Low-Voltage Microcontroller

DS97LVO0701

2-21

RAM. The Z86L78 has 512-bytes of RAM and 256 bytes

make-up the Register file. The remaining 256 bytes make

up the Extended Data RAM.

Extended Data RAM. The Extended Data RAM occupies

the address range. FF00H-FFFFH (256 bytes). Accessing

the Extended Data RAM is accomplished by using LDE in-

struction only.

Note: The Extended Data RAM cannot be used as Stack

or instructions/code memory.

Expanded Register File (ERF). The standard Z8 register

file has been expanded to allow for additional system con-

trol registers, and for mapping of additional peripheral de-

vices along with I/O ports into the register address area.

The Z8 register address space R0 through R15 has been

implemented as 16 groups of 16 registers per group.

These register groups are known as the Expanded Regis-

ter File (ERF). Bits 7-4 of register RP select the working

The upper nibble of the register pointer (Figure 18) selects

which group of 16 bytes in the register file, out of the full

256 bytes, will be accessed. The lower nibble selects the

expanded register file bank and, in the case of the Z86L78,

Banks F and D are implemented. A 0H in the lower nibble

will allow the normal register file to be addressed, but any

other value from 1H to FH will exchange the lower 16 reg-

isters in favor of an expanded register group of 16 regis-

ters.

For example:

Z86L78: (See Figure 17)

R253 RP = 00H

R0 = Port 0

R1 = Port 1

R2 = Port 2

R3 = Port 3

But if:

R253 RP = 0DH

R0 = CTRL0

R1 = CTRL1

R2 = CTRL2

R3 = Reserved

The counter/timers are mapped into ERF group D. Access

is easily done using the following example:

LD RP, #0DH Select ERF D for access and register Bank

0 as the working register group

LD R0,#xx access CTRL0

LD1, #xx access CTRL1

LDRP, #7DH Select expanded register group (ERF) group

D for access and register Bank 7 as the working reg-

ister bank

LDR1, 2 CTRL2

→ register 71H

Figure 15. Register Pointer Register

D4 D3

D1 D0

Expanded Register

File Pointer

Working Register

Pointer

R253 RP

Default Setting After Reset = 0000 0000

Z86L78 Datasheet(PDF) 21 Page - Zilog, Inc.

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