Z86C21 Datasheet, PDF (14/35 Pages) Zilog, Inc. – 8K ROM Z8 CMOS MICROCONTROLLER

FUNCTIONAL DESCRIPTION (Continued)
REGISTER POINTER
D7 D6 D5 D4 0 0 0 0
Working Register
Group Pointer
Z8 REGISTER FILE
%FF
%F0
%7F
Z86C21 MCU
WITH 8K ROM
Z8 STANDARD CONTROL REGISTERS
REGISTER
% FF
% FE
% FD
% FC
% FB
% FA
% F9
† % F8
% F7
% F6
% F5
% F4
% F3
% F2
% F1
% F0
SPL
SPH
RP
FLAGS
IMR
IRQ
IPR
P01M
P3M
P2M
PRE0
T0
PRE1
T1
TMR
S10
RESET CONDITION
D7 D6 D5 D4 D3 D2 D1 D0
UUUUUU U U
UUUUUU U U
UUUUUU U U
UUUUUU U U
0 UUUUU U U
000000 0 0
UUUUUU U U
010011 0 1
000000 0 0
111111 1 1
UUUUUU U 0
UUUUUU U U
UUUUUU 0 0
UUUUUU U U
000000 0 0
UUUUUU U U
%0F
%00
Notes:
1. General-purpose registers are not reset
after Stop-Mode Recovery or after a Reset.
2. General-purpose registers are undefined
after Power-up.
REGISTER
% (0) 03
P3
% (0) 02
P2
% (0) 01
P1
% (0) 00
P0
RESET CONDITION
1 1 1 1 UU U U
UU U U UU U U
UU U U UU U U
UU U U UU U U
U = Unknown
† = For ROMless (Z86C91) reset condition = 10110110
Figure 14. RAM Register File Reset Condition
RAM Protect. The upper portion of the RAM’s address
spaces 80FH to EFH (excluding the control registers) can
be protected from reading and writing. The RAM Protect bit
option is mask-programmable and is selected by the
customer when the ROM code is submitted. After the mask
option is selected, the user activates from the internal ROM
code to turn off/on the RAM Protect by loading a bit D6 in
the IMR register to either a 0 or a 1, respectively. A 1 in D6
indicates RAM Protect enabled.
ROM Protect. The first 8 Kbytes of program memory is
mask programmable. A ROM protect feature prevents
dumping of the ROM contents by inhibiting execution of
LDC, LDCI, LDE, and LDEI instructions to Program Memory
in all modes.
The ROM Protect option is mask-programmable, to be
selected by the customer at the time when the ROM code
is submitted.
Note: With RAM/ROM protect on, the Z86C21 cannot
access the memory space.
Stack. The Z86C21 has a 16-bit Stack Pointer (R254-
R255) used for external stack that resides anywhere in the
data memory for the ROMless mode, but only from 8192
to 65535 in the ROM mode. An 8-bit Stack Pointer (R255)
is used for the internal stack that resides within the 236
general-purpose registers (R4-R239). The high byte of the
Stack Pointer (SPH-Bit 8-15) is used as a general-purpose
register when using internal stack only.
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