Force
Load
Input
Mode
TOD
A
strobe bit allows the timer latch to be loaded into the timer
counter at any time, whether the timer is running or not.
Control bits allow selection of the clock used to decrement the timer.
TIMER
A
can count 02 pulses or external pulses applied to the CNT
pin. TIMER
B
can count 02 pulses, external CNT pulses, TIMER
A
un-
derflow pulses or TIMER
A
underflow pulses while the CNT pin is
held high.
The timer latch is loaded into the timer on any timer underflow, on a
force load or following a write to the high byte of the prescaler while
the timer is stopped. If the timer is running, a write to the high byte
will load the timer latch, but not reload the counter.
READ (TIMER)
REG Name
4 TA
L0
TA17
5
TAHI TAH7
6
TB
L0
TBL7
7
TB
HI
TBH7
WRITE (PRESCALER)
REG Name
4 TA
L0
PAL7
5
TA HI PAH7
6
TB
L0
PBL7
7
TB HI
PBH7
TA16
TA15 TA14
TAL3 TAL2
TAL1
TALO
TAH6 TAH5
TAH4
TAH3
TAH2
TAHl
TAHO
TBL6
TB15
TB14
TBL3 TBL2
TBLl
TBLO
TBH6
TBH5
TBH4
TBH3
TBH2
TBHl
TBHO
PAL6
PAL5
PAL4 PAL3
PAL2
PAL1
PAL0
PAH6 PAH5
PAH4
PAH3
PAH2
PAHl
PAHO
PBL6
PBL5
PBL4
PBL3
PBL2
PBLl
PBLO
PBH6
PBH5
PBH4
PBH3
PBH2
PBHl
PBHO
TOD consists of a 24 bit binary counter. Positive edge transitions on
this pin cause the binary to increment. The TOD pin has a passive
pull-up on it.
A
programmable
ALARM
is provided for generating an
interrupt at a desired time. The
ALARM
registers are located at the
same addresses as the corresponding TOD register. Access to the
ALARM
is governed by a Control Register bit. The
ALARM
is write-
only; any read of a TOD address will read time regardless of the state
of the
ALARM
access bit.
A
specific sequence of events must be followed for proper setting
and reading of
TOD. TOD is automatically stopped whenever a write
to the register occurs. The clock will not start again until after a
write to the LSB Event Register. This assures TOD will always start
at the desired time. Since a carry from one stage to the next can oc-
cur at any time with respect to
a
read operation, a latching function
is included to keep all Time of Day information constant during a
To Next Page
Loading...
