Intel 8253 - Page 118

Philips Semiconductors Product specification
80C31/80C32
80C51 8-bit microcontroller family
128/256 byte RAM ROMless low voltage (2.7V–5.5V),
low power, high speed (33 MHz)
2000 Aug 07
12
÷12
C/T2 = 0
C/T2
= 1
TL2 TH2
TR2
CONTROL
T2 PIN
SU00730
FFH FFH
RCAP2L RCAP2H
(UP COUNTING RELOAD VALUE) T2EX PIN
TF2
INTERRUPT
COUNT
DIRECTION
1 = UP
0 = DOWN
EXF2
OVERFLOW
(DOWN COUNTING RELOAD VALUE)
TOGGLE
OSC
Figure 5. Timer 2 Auto Reload Mode (DCEN = 1)
OSC
÷ 2
C/T2 = 0
C/T2
= 1
TR2
Control
TL2
(8-bits)
TH2
(8-bits)
÷ 16
RCAP2L RCAP2H
EXEN2
Control
EXF2
Timer 2
Interrupt
T2EX Pin
Transition
Detector
T2 Pin
Reload
NOTE: OSC. Freq. is divided by 2, not 12.
÷ 2
“0” “1”
RX Clock
÷ 16 TX Clock
“0”“1”
“0”“1”
Timer 1
Overflow
Note availability of additional external interrupt.
SMOD
RCLK
TCLK
SU00068
Figure 6. Timer 2 in Baud Rate Generator Mode