cop8acc National Semiconductor Corporation, cop8acc Datasheet - Page 20

• Manufacturer Part Number: cop8acc
• Description: 8-bit Cmos Rom Based And Otp Microcontrollers With 4k Or 16k Memory And High Resolution A/d
• Manufacturer: National Semiconductor Corporation

www.national.com
Multi-Input Wakeup
A control flag, LPEN, functions as a global interrupt enable
for Port L interrupts. Setting the LPEN flag will enable inter-
rupts and vice versa. A separate global pending flag is not
needed since the register WKPND is adequate.
Since Port L is also used for waking the devices out of the
HALT or IDLE modes, the user can elect to exit the HALT or
IDLE modes either with or without the interrupt enabled. If he
elects to disable the interrupt, then the devices will restart
execution from the instruction immediately following the in-
struction that placed the microcontroller in the HALT or IDLE
modes. In the other case, the devices will first execute the
interrupt service routine and then revert to normal operation.
(See HALT MODE for clock option wakeup information.)
Analog Function Block
This device contains an analog function block with the intent
to provide a function which allows for single slope, low cost,
A/D conversion of up to 6 channels.
CMPSL REGISTER (ADDRESS X’00B7)
The CMPSL register contains the following bits:
CMPT2B
CMPISEL0/1/2 Will select one of seven possible sources
CMPT2B
Bit 7
CMPISEL2
Selects the “High Speed 16-bit Capture
Timer” input to be driven directly by the
comparator output. If the comparator is dis-
abled (CMPEN=0), this function is dis-
abled, i.e. the Capture Timer input is con-
nected to GND.
(I0/I2/I3/I4/I5/I6/internal reference) as a
positive input to the comparator (see Table
4 for more information)
CMPISEL1
CMPISEL0
(Continued)
CMPOE
CSEN
FIGURE 13. Analog Function Block
CMPEN
CMPNEG
Bit 0
20
CMPOE
CSEN
CMPEN
CMPNEG
The Comparator Select Register is cleared on RESET (the
comparator is disabled). To save power the program should
also disable the comparator before the µC enters the HALT/
IDLE modes. Disabling the comparator will turn off the con-
stant current source and the V
comparator output from the Capture Timer input and pin I3/I7
and remove the low on I1 caused by CMPNEG.
It is often useful for the user’s program to read the result of
a comparator operation. Since I1 is always selected to be
COMPIN — when the comparator is enabled (CMPEN=1),
the comparator output can be read internally by reading bit 1
(CMPRD) of register PORTI (RAM address 0xD7).
The following table lists the comparator inputs and outputs
versus the value of the CMPISEL0/1/2 bits. The output will
only be driven if the CMPOE bit is set to 1.
Enables the comparator output to either pin
I3 or pin I7 (“1”=enable) depending on the
value of CMPISEL0/1/2.
Enables the internal constant current
source. This current source provides a
nominal 20 µA constant current at the I1
pin. This current can be used to ensure a
linear charging rate on an external capaci-
tor. This bit has no affect and the current
source is disabled if the comparator is not
enabled (CMPEN=0).
Enable the comparator (“1” = enable)
Will drive I1 to a low level. This bit can be
used to discharge an external capacitor.
This bit is disabled if the comparator is not
enabled (CMPEN=0).
CC
/2 reference, disconnect the
DS012865-61