MAXQ612/MAXQ622 User’s Guide
Maxim Integrated 4-5
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.
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