COPCH942C Datasheet, PDF (16/26 Pages) National Semiconductor (TI) – 8-Bit CMOS ROM Based Microcontrollers with 1k or 2k

Functional Description (Continued)
MODE 1. TIMER WITH AUTO-LOAD REGISTER
In this mode of operation, the timer T1 counts down at the in-
struction cycle rate. Upon underflow the value in the register
R1 gets automatically reloaded into the timer which contin-
ues to count down. The timer underflow can be programmed
to interrupt the microcontroller. A bit in the control register
CNTRL enables the TIO (G3) pin to toggle upon timer under-
flows. This allow the generation of square-wave outputs or
pulse width modulated outputs under software control. (See
Figure 8)
MODE 2. EXTERNAL COUNTER
In this mode, the timer T1 becomes a 16-bit external event
counter. The counter counts down upon an edge on the TIO
pin. Control bits in the register CNTRL program the counter
to decrement either on a positive edge or on a negative
edge. Upon underflow the contents of the register R1 are au-
tomatically copied into the counter. The underflow can also
be programmed to generate an interrupt. (See Figure 8)
MODE 3. TIMER WITH CAPTURE REGISTER
Timer T1 can be used to precisely measure external fre-
quencies or events in this mode of operation. The timer T1
counts down at the instruction cycle rate. Upon the occur-
rence of a specified edge on the TIO pin the contents of the
timer T1 are copied into the register R1. Bits in the control
register CNTRL allow the trigger edge to be specified either
as a positive edge or as a negative edge. In this mode the
user can elect to be interrupted on the specified trigger edge.
(See Figure 9.)
FIGURE 7. MICROWIRE/PLUS Application
CNTRL
Bits
765
000
001
010
011
100
101
110
111
TABLE 5. Timer Operating Modes
Operation Mode
External Counter W/Auto-Load Reg.
External Counter W/Auto-Load Reg.
Not Allowed
Not Allowed
Timer W/Auto-Load Reg.
Timer W/Auto-Load Reg./Toggle TIO Out
Timer W/Capture Register
Timer W/Capture Register
T Interrupt
Timer Underflow
Timer Underflow
Not Allowed
Not Allowed
Timer Underflow
Timer Underflow
TIO Pos. Edge
TIO Neg. Edge
DS009103-13
Timer
Counts
On
TIO Pos. Edge
TIO Neg. Edge
Not Allowed
Not Allowed
t_C
t_C
t_C
t_C
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