NT6868A Datasheet, PDF (4/14 Pages) List of Unclassifed Manufacturers – Keyboard Controller

NT6868A
System Reserved Registers
Address
$00C0
$00C1
Register
BT
TCON
$00C2
$00C3
$00C4
$00C5
$00C6
$00C7
$00C8
$00C9
$00CA
$00CB
$00CC
$00CD
$00CE
$00CF
CLRIRQX
PORT0
PORT1
PORT2
PORT3
CLK
DATA
LED
CLRWDT
X
X
X
X
X
Bit7
BT7
-
-
PD07
PD17
PD27
-
-
-
-
0
X
X
X
X
X
Bit6
BT6
-
-
PD06
PD16
PD26
-
-
-
-
1
X
X
X
X
X
Bit5
BT5
-
-
PD05
PD15
PD25
-
-
-
-
0
X
X
X
X
X
Bit4
BT4
-
-
PD04
PD14
PD24
PD34
-
-
-
1
X
X
X
X
X
Bit3
BT3
-
-
PD03
PD13
PD23
PD33
-
-
-
0
X
X
X
X
X
Bit2
BT2
-
-
PD02
PD12
PD22
PD32
-
-
LED2
1
X
X
X
X
X
Bit1
Bit0
BT1
BT0
W
-
ENBT
W
-
CLRIRQTMR W
PD01
PD00
RW
PD11
PD10
RW
PD21
PD20
RW
PD31
PD30
RW
-
CLK
RW
-
DATA
RW
LED1
LED0
W
0
1
W
X
X
X
X
X
X
X
X
X
X
X
X
X
X
X
- : no effect
X : access not allowed
4K X 8 ROM
Power-On Reset
The built-in ROM program code, executed by the 6502
CPU, has a capacity of 4K X 8 bits and is addressed
from F000H to FFFFH.
128 X 8 SRAM
Built-in power-on reset circuit can generate a 150ms
pulse to reset the entire chip. The beginning of the
150ms pulse occurs at 60% of VDD when powered on.
The built-in SRAM is used for general purpose data
memory and for the stack area. SRAM is addressed from
0000H to 007FH. User can allocate stack area in the
SRAM by setting stack pointer register (S). Because the
6502C default stack pointer is 01FFH, it must be
mapped to 007FH. Mapping from 01XX to 00XX is done
internally by setting the S register to 7FH via software
programming.
For example :
power
VDD
60%
The start of 150ms pulse
t
LDX #$7F
TXS
4