HT45R22E Holtek Semiconductor, HT45R22E Datasheet - Page 52

• Manufacturer Part Number: HT45R22E
• Description: Remote Type 8-bit OTP MCU
• Manufacturer: Holtek Semiconductor

Interrupts often occur in an unpredictable manner or
need to be serviced immediately in some applications. If
only one stack is left and the interrupt is not well con-
trolled, the original control sequence will be damaged
once a CALL subroutine is executed in the interrupt
subroutine.
All of these interrupts have the capability of waking up
the processor when in the Idle/Sleep Mode.
Only the Program Counter is pushed onto the stack. If
the contents of the register or status register are altered
by the interrupt service program, which may corrupt the
desired control sequence, then the contents should be
saved in advance.
LCD SCOM Function
The devices have the capability of driving external LCD
panels. The common pins for LCD driving, SCOM0~
SCOM3, are pin shared with certain pin on the PB0~
PB3 port. The LCD signals (COM and SEG) are gener-
ated using the application program.
LCD Operation
An external LCD panel can be driven using this device
by configuring the PB0~PB3 pins as common pins and
using other output ports lines as segment pins. The LCD
driver function is controlled using the SCOMC register
which in addition to controlling the overall on/off function
also controls the bias voltage setup function. This en-
ables the LCD COM driver to generate the necessary
V
Rev. 1.00
DD
/2 voltage levels for LCD 1/2 bias operation.
52
The SCOMEN bit in the SCOMC register is the overall
master control for the LCD Driver, however this bit is
used in conjunction with the COMnEN bits to select
which Port B pins are used for LCD driving. Note that the
Port Control register does not need to first setup the pins
as outputs to enable the LCD driver operation.
LCD Bias Control
The LCD COM driver enables a range of selections to
be provided to suit the requirement of the LCD panel
which is being used. The bias resistor choice is imple-
mented using the ISEL1 and ISEL0 bits in the SCOMC
register.
SCOMEN
0
1
1
COMnEN
X
0
1
Output Control
SCOM Circuit
Pin Function
SCOMN
I/O
I/O
HT45R22E
March 17, 2010
O/P Level
www.DataSheet4U.com
0 or 1
0 or 1
V
DD
/2