T48C893 Datasheet, PDF (43/82 Pages) ATMEL Corporation – The multiple times programmable (MTP) version for the MARC4 ROM types

TOG2 T3I
Control
T48C893
T3EIM
INT5
Capture register
CL3
RES
8-bit counter
D
NQ
T3SM1 T3RM1
CM31
8-bit comparator
Control ^C31
C32
CM32
T3IM1
T3TM1 : T3M1
TOG3
Compare register 1
Compare register 2
NQ
D
T3SM2 T3RM2
Figure 45. Counter 3 stage
T3IM2
T3TM2 ^{: T3M2}
13809
Timer / Counter Modes
Timer 3 has 6 timer modes and 6 modulator/demodulator
modes. The mode is set via the Timer 3 Mode Register
T3M.
In all these modes, the compare register and the compare-
mode register belonging to it define the counter value for
a compare match and the action of a compare match. A
match of the current counter value with the content of one
compare register triggers a counter reset, a Timer 3
interrupt or the toggling of the output flip-flop. The
compare mode registers T3M1 and T3M2 contain the
mask bits for enabling or disabling these actions.
The counter can also be enabled to execute single actions
with one or both compare registers. If this mode is set the
corresponding compare match event is generated only
once after the counter start.
Most of the timer modes use its compare registers
alternately. After the start has been activated, the first
comparison is carried out via the compare register 1,
the second is carried out via the compare register 2, the
third is carried out again via the compare register 1
and so on. This makes it easy to generate signals with
constant periods and variable duty cycle or to generate
signals with variable pulse and space widths.
If single-action mode is set for one compare register, the
comparison is always carried out after the first cycle via
the other compare register.
The counter can be started and stopped via the control
register T3C. This register also controls the initial level
of the output before start. T3C contains the interrupt mask
for a T3I input interrupt.
Via the Timer 3 clock-select register, the internal or
external clock source can be selected. This register selects
also the active edge of the external input. An edge at the
external input T3I can generate also an interrupt if the
T3EIM-bit is set and the Timer 3 is stopped (T3R = 0) in
the T3C-register.
The status of the timer as well as the occurrence of a
compare match or an edge detect of the input signal is
indicated by the status register T2ST. This allows
identification of the interrupt source because all these
events share only one timer interrupt.
Timer 3 compare data values
The Timer 3 has two 8-bit compare registers (T3CO1,
T3CO2). The compare data value can be ‘m’ for each of
the Timer 3 compare registers.
The compare data value for the compare registers is:
m = x +1 0 ≤ x ≤ 255
Rev. A4, 22-Jan-02
43 (82)