AT89S8252-24QC ATMEL [ATMEL Corporation], AT89S8252-24QC Datasheet - Page 10

• Manufacturer Part Number: AT89S8252-24QC
• Description: 8-bit Microcontroller with 8K Bytes Flash
• Manufacturer: ATMEL [ATMEL Corporation]

the transition was detected. Since two machine cycles (24
oscillator periods) are required to recognize a 1-to-0 transi-
tion, the maximum count rate is 1/24 of the oscillator
frequency. To ensure that a given level is sampled at least
once before it changes, the level should be held for at least
one full machine cycle.
Table 8. Timer 2 Operating Modes
Figure 1. Timer 2 in Capture Mode
10
RCLK + TCLK
T2EX PIN
0
0
1
X
OSC
T2 PIN
CP/RL2
0
1
X
X
AT89S8252
÷12
TRANSITION
DETECTOR
TR2
1
1
1
0
MODE
16-bit Auto-reload
16-bit Capture
Baud Rate Generator
(Off)
C/T2 = 0
C/T2 = 1
EXEN2
TR2
CAPTURE
CONTROL
CONTROL
Capture Mode
In the capture mode, two options are selected by bit
EXEN2 in T2CON. If EXEN2 = 0, Timer 2 is a 16 bit timer
or counter which upon overflow sets bit TF2 in T2CON.
This bit can then be used to generate an interrupt. If
EXEN2 = 1, Timer 2 performs the same operation, but a l-
to-0 transition at external input T2EX also causes the cur-
rent value in TH2 and TL2 to be captured into RCAP2H and
RCAP2L, respectively. In addition, the transition at T2EX
causes bit EXF2 in T2CON to be set. The EXF2 bit, like
TF2, can generate an interrupt. The capture mode is illus-
trated in Figure 1.
RCAP2H
TH2
EXF2
RCAP2L
TL2
OVERFLOW
TF2
INTERRUPT
TIMER 2