Z86L81 Datasheet, PDF (31/88 Pages) Maxim Integrated Products – 28-Pin Low-Voltage Infrared Microcontrollers

Z86L81/86/98
28-Pin Low-Voltage Infrared Microcontrollers
25
The upper nibble of the register pointer (see Figure 12) selects which working reg-
ister group, of 16 bytes in the register file, is accessed out of the possible 256. The
lower nibble selects the expanded register file bank and, in the case of the
Z86L81/86/98 family, banks 0, F, and D are implemented. A 0h in the lower nibble
allows the normal register file (bank 0) to be addressed, but any other value from
1h to Fh exchanges the lower 16 registers to an expanded register bank.
R253 RP
D7 D6 D5 D4 D3 D2 D1 D0
Default Setting After Reset = 0000 0000
Expanded Register
File Pointer
Working Register
Pointer
Figure 12. Register Pointer
Example: Z86L81/86/98: (See Figure 11 on page 24)
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 performed
using the following:
LD RP, #0Dh
; Select ERF D for access to bank D
(working register group 0)
LD R0,#xx
; load CTRL0
LD 1, #xx
; load CTRL1
LD R1, 2
; CTRL2CTRL1
19-4615; Rev 0; 4/09