Z86L70 Datasheet, PDF (20/61 Pages) Zilog, Inc. – IR/Low-Voltage Microcontroller

Z86L70/71/75/C71
IR/Low-Voltage Microcontroller
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
register address area. The Z8 register address space R0
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
register bank is also referred to as expanded register
group (Figure14).
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
register bank.
Zilog
For example:
Z86L70: (See Figure 16)
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 to bank D ( work-
ing register group 0)
LD R0,#xx load CTRL0
LD 1, #xx
load CTRL1
LD R1, 2
CTRL2 → CTRL1
LD RP, #7DH Select expanded register bank D and
working register group 7 of bank 0 for access .
LD 71H, 2
CTRL2 → register 71H
LD R1, 2
CTRL2 → register 71H
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PRELIMINARY
DS97LVO0500