80C154/83C154
Figure 6. External Drive Configuration.
Hardware Description
Same as for the 80C51, plus a third timer/counter :
EXEN2 = 0, then when Timer 2 rolls over it does not only
set TF2 but also causes the Timer 2 register to be reloaded
with the 16 bit value in registers RCAP2L and RCAP2H,
which are preset by software. If EXEN2 = 1, then Timer
2 still does the above, but with the added feature that a
1-to-0 transition at external input T2EX will also trigger
the 16 bit reload and set EXF2.
Timer/Event Counter 2
Timer 2 is a 16 bit timer/counter like Timers 0 and 1, it
can operate either as a timer or as an event counter. This
is selected by bit C/T2 in the Special Function Register
T2CON (Figure 1). It has three operating modes :
“capture”, “autoload” and “baud rate generator”, which
are selected by bits in T2CON as shown in Table 2.
The auto-reload mode is illustrated in Figure 8.
Figure 7. Timer 2 in Capture Mode.
Table 2.Timer 2 Operating Modes.
RCLK +
CP/RL2
TR2
MODE
TCLK
0
0
1
0
1
X
X
1
1
1
0
16 bit auto-reload
16 bit capture
baud rate generator
(off)
X
In the capture mode there are two options which are
selected by bit EXEN2 in T2CON; If EXEN2 = 0, then
Timer 2 is a 16 bit timer or counter which upon
overflowing sets bit TF2, the Timer 2 overflow bit, which
can be used to generate an interrupt. If EXEN2 = 1, then
Timer 2 still does the above, but with the added feature
that a 1-to-0 transition at external input T2EX causes the
current value in the Timer 2 registers, TL2 and TH2, to
be captured into registers RCAP2L and RCAP2H,
respectively. In addition, the transition at T2EX causes bit
EXF2 in T2CON to be set, and EXF2, like TF2, can
generate an interrupt.
Figure 8. Timer 2 in Auto-Reload Mode.
The capture mode is illustrated in Figure 7.
In the auto-reload mode there are again two options,
which are selected by bit EXEN2 in T2CON.If
8
MATRA MHS
Rev.F (14 Jan. 97)
TEMIC [ TEMIC SEMICONDUCTORS ]
