L8708H datasheet(27/66 Pages) ZILOG

27 / 66 page

Z86L88/81/86/87/89/73

IR/Low-Voltage Microcontroller

DS96LV00800

P R E L I M I N A R Y

Expanded Register File. The register file has been ex-

panded to allow for additional system control registers,

and for mapping of additional peripheral devices into the

through R15 has been implemented as 16 banks of 16 reg-

isters per bank. These register groups are known as the

ERF (Expanded Register File). Bits 7-4 of register RP se-

lect the working register group. Bits 3-0 of register RP se-

lect the expanded register file bank. Note that expanded

also referred to as expanded register

group (Figure 21).

The upper nibble of the register pointer (Figure 23) selects

which working register group of 16 bytes in the register file,

out of the possible 256, will be accessed. The lower nibble

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

the Z86LXX family, banks 0, F, and D are implemented. A

0h in the lower nibble will allow the normal register file

(bank 0) to be addressed, but any other value from 1h to

Fh will exchange the lower 16 registers to an expanded

For example:

Z86L73: (See Figure 21)

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:

RP, #0Dh Select ERF D for access to bank D ( work-

ing register group 0)

R0,#xx

load CTRL0

1, #xx

load CTRL1

R1, 2

CTRL2

→ CTRL1

RP, #7Dh

Select expanded register bank D and

working register group 7 of bank 0 for access .

71h, 2

CTRL2

→ register 71h

R1, 2

CTRL2

→ register 71h

L8708H Datasheet(PDF) 27 Page - Zilog, Inc.

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