EM78808
8-bit Micro-controller
duty
1/8
1/9
1/16
1/24
COM0 ~ COM7
COM8 COM9
..
..
..
..
..
COM15 COM15 ~ COM23
o
o
o
o
X
O
O
O
x
x
o
o
x
x
o
o
x
x
x
o
x : open, o : select
SEG signal : The segment signal pins are connected to the corresponding display RAM. The high byte to the
low byte Bit 0 ~ Bit 7 are correlated to COM0 ~ COM23 respectively . When a bit of display RAM
is 1, a select signal is sent to the corresponding segment pin, and when the bit is 0 , a non-select
signal is sent to the corresponding segment pin.
Bit 4(KEYSCAN) : Key scan function enable control bit
0/1 ꢂdisable/enable
If you enable key scan function LCD waveform will has a small pulse within a period like Fig.13.
V1
V2
V4
V5
COM2
GND
V1
V2
V4
SEG
V5
GND
V1
V2
V4
V5
30us
GND
Fig.13. key scan waveform for 1/8, 1/9, 1/16 duty
Bit 5(KEYSTRB) : Key strobe enable control bit
0/1 ꢂdisable/enable
key strobe signal , if you set this bit , segment will switch to strobe signal temporally and output zero
signal ( one instruction long ) one by one from segment 8 to segment 23. During one segment strobe time,
CPU will check port7(0:3) equal to "1111" or not. If not, CPU will latch a zero at IOC7 PAGE1 and IOC8
PAGE1 one by one depends on which segment strobe.
After strobe, this bit will be cleared . Fig.14 is key strobe signal.
______________________________________________________________________________________________________________________________________________________
* This specification is subject to change without notice.
8/1/2004 (V3.1)
26
ELAN [ ELAN MICROELECTRONICS CORP ]
