Z86D990 Datasheet, PDF (65/102 Pages) Zilog, Inc. – Low-Voltage Micro controllers with ADC

Z86D990/Z86D991 OTP and Z86L99X ROM
Low-Voltage Microcontrollers with ADC
58
Table 15. FLAGS Register [Group/Bank F0h, Register C (R252)] (Continued)
____3___ Decimal Adjust R/W 1
Flag (D)
0
_____2__ Half Carry
Flag (H)
R/W 1
0
______1_ User Flag (F2) R/W 1
0
_______0 User Flag (F1) R/W 1
0
Used for BCD arithmetic—after a
subtraction, the flag is set to 1;
following an addition, it is cleared to 0
Set to 1, whenever an addition
generates a “carry out” of bit position
3 (overflow) of an accumulator; or
subtraction generates a “borrow into”
bit 3
User definable
User definable
Register Pointer (RP)
Z8 instructions can access registers directly or indirectly using either a 4-bit or 8-
bit address field. The upper nibble of the Register Pointer, as described in
Table 16, contains the base address of the active Working Register GROUP. The
lower nibble contains the base address of the Expanded Register File BANK.
When using 4-bit addressing, the 4-bit address of the working register (r0 to rF) is
combined with the upper nibble of the Register Pointer (identifying the WR
GROUP), thus forming the 8-bit actual address.
Table 16. RP Register [Group/Bank F0h, Register D (R253)]
Bit
7
6
5
4
Bit/Field Working Register Group
R/W
R/W R/W R/W R/W
Reset
0
0
0
0
R = Read, W = Write, X = Indeterminate
Bit
Position
Bit/Field
R/W Value
7654_____ Working Register R/W X
Group Pointer
_____3210 Expanded
Register File
Bank Pointer
R/W X
3
2
1
0
Expanded Register File Bank
R/W R/W R/W R/W
0
0
0
0
Description
Identifies 1 of 16 possible WR
Groups, each containing 16 Working
Registers
Identifies 1 of 16 possible ERF
Banks; only Banks 0, D, and F are
valid for the Z86D99/Z86L99 family
PS003807-1002
PRELIMINARY