at89c5131 ATMEL Corporation, at89c5131 Datasheet - Page 50

• Manufacturer Part Number: at89c5131
• Description: 8-bit Flash Microcontroller With Full Speed Usb Device At89c5131
• Manufacturer: ATMEL Corporation

Timer 2
Auto-reload Mode
4136C–USB–04/05
The Timer 2 in the AT89C5131 is the standard C52 Timer 2. It is a 16-bit timer/counter:
the count is maintained by two cascaded eight-bit timer registers, TH2 and TL2. It is
controlled by T2CON (Table 47) and T2MOD (Table 48) registers. Timer 2 operation is
similar to Timer 0 and Timer 1. C/T2 selects F
(counter operation) as the timer clock input. Setting TR2 allows TL2 to be incremented
by the selected input.
Timer 2 has 3 operating modes: capture, auto reload and Baud Rate Generator. These
modes are selected by the combination of RCLK, TCLK and CP/RL2 (T2CON).
Refer to the Atmel 8-bit microcontroller hardware documentation for the description of
Capture and Baud Rate Generator Modes.
Timer 2 includes the following enhancements:
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•
The Auto-reload mode configures Timer 2 as a 16-bit timer or event counter with auto-
matic reload. If DCEN bit in T2MOD is cleared, Timer 2 behaves as in 80C52 (refer to
the Atmel 8-bit microcontroller hardware description). If DCEN bit is set, Timer 2 acts as
an Up/down timer/counter as shown in Figure 23. In this mode the T2EX pin controls the
direction of count.
When T2EX is high, Timer 2 counts up. Timer overflow occurs at FFFFh which sets the
TF2 flag and generates an interrupt request. The overflow also causes the 16-bit value
in RCAP2H and RCAP2L registers to be loaded into the timer registers TH2 and TL2.
When T2EX is low, Timer 2 counts down. Timer underflow occurs when the count in the
timer registers TH2 and TL2 equals the value stored in RCAP2H and RCAP2L registers.
The underflow sets TF2 flag and reloads FFFFh into the timer registers.
The EXF2 bit toggles when Timer 2 overflows or underflows according to the direction of
the count. EXF2 does not generate any interrupt. This bit can be used to provide 17-bit
resolution.
Auto-reload mode with up or down counter
Programmable Clock-output
OSC
/12 (timer operation) or external pin T2
AT89C5131
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