COP880C Datasheet, PDF (15/31 Pages) National Semiconductor (TI) – Microcontrollers

Functional Description (Continued)
TABLE 4.
G4
Config.
Bit
1
0
1
0
G5
Config.
Bit
1
1
0
0
G4
Fun.
SO
TRI-STATE
SO
TRI-STATE
G5
Fun.
Int.
SK
Int.
SK
Ext.
SK
Ext.
SK
G6
Fun.
SI
SI
SI
SI
Operation
MICROWIRE
Master
MICROWIRE
Master
MICROWIRE
Slave
MICROWIRE
Slave
TIMER/COUNTER
The device has a powerful 16-bit timer with an associated
16-bit register enabling them to perform extensive timer
functions. The timer T1 and its register R1 are each orga-
nized as two 8-bit read/write registers. Control bits in the
register CNTRL allow the timer to be started and stopped
under software control. The timer-register pair can be oper-
ated in one of three possible modes. Table 5 details various
timer operating modes and their requisite control settings.
DS010802-9
FIGURE 7. MICROWIRE/PLUS Block Diagram
MODE 1. TIMER WITH AUTO-LOAD REGISTER
In this mode of operation, the timer T1 counts down at the
instruction cycle rate. Upon underflow the value in the reg-
ister R1 gets automatically reloaded into the timer which
continues to count down. The timer underflow can be pro-
grammed to interrupt the microcontroller. A bit in the control
register CNTRL enables the TIO (G3) pin to toggle upon
timer underflows. This allow the generation of square-wave
outputs or pulse width modulated outputs under software
control. (See Figure 9.)
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
automatically copied into the counter. The underflow can
also be programmed to generate an interrupt. (See Figure 9)
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 10.)
15
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