Maxim Integrated MAXQ610 - Manual (Page 60)

4-5
MAXQ610 User’s Guide
4.1 System Register Descriptions
The addresses for each register are given in the format module[index], where module is the module specifier from 08h
to 0Fh and index is the register subindex from 00h to 0Fh .
REGISTER DESCRIPTION
AP, 08h[00h] Accumulator Pointer Register (8 bits)
Initialization This register is cleared to 00h on all forms of reset .
Access Unrestricted direct read/write access .
AP.3 to AP.0 Active Accumulator Select. These bits select which of the 16 accumulator registers are
used for arithmetic and logical operations . If the APC register has been set to perform
automatic increment/decrement of the active accumulator, this setting is automatically
changed after each arithmetic or logical operation . If a ‘MOVE AP, Acc’ instruction is exe-
cuted, any enabled AP inc/dec/modulo control takes precedence over the transfer of Acc
data into AP .
AP.7 to AP.4 Reserved . All reads return 0 .
APC, 08h[01h] Accumulator Pointer Control Register (8 bits)
Initialization This register is cleared to 00h on all forms of reset .
Access Unrestricted direct read/write access .
APC.2 to APC.0
(MOD2 to MOD0) Accumulator Pointer Auto Increment/Decrement Modulus. If these bits are set to a non-
zero value, the accumulator pointer (AP[3:0]) is automatically incremented or decremented
following each arithmetic or logical operation .
The mode for the autoincrement/decrement is determined as follows:
MOD[2:0] AUTOINCREMENT/DECREMENT MODE
000 No autoincrement/decrement (default)
001 Increment/decrement AP[0] modulo 2
010 Increment/decrement AP[1:0] modulo 4
011 Increment/decrement AP[2:0] modulo 8
100 Increment/decrement AP modulo 16
101 to 111 Reserved (modulo 16 when set)
APC.5 to APC.3 Reserved . All reads return 0 .
APC.6 (IDS) Increment/Decrement Select. If this bit is set to 0, the accumulator pointer, AP, is incre-
mented following each arithmetic or logical operation according to MOD[2:0] .
If this bit is set to 1, the accumulator pointer, AP, is decremented following each arithmetic
or logical operation according to MOD[2:0] .
If MOD[2:0] is set to 000, the setting of this bit is ignored .
APC.7 (CLR) AP Clear. Writing this bit to 1 clears the accumulator pointer, AP, to zero . If a ‘MOVE APC,
Acc’ instruction is executed requesting that AP be set to zero (i .e ., CLR = 1), the AP clear
function overrides any enabled inc/dec/modulo control . All reads from this bit return 0 .