Datasheet

53
4337K–USB–04/08
AT89C5130A/31A-M
13. Timer 2
The Timer 2 in the AT89C5130A/31A-M 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 13-1) and T2MOD (Table 13-2) registers. Timer 2 operation is similar to Timer
0 and Timer 1. C/T2 selects F
OSC
/12 (timer operation) or external pin T2 (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:
• Auto-reload mode with up or down counter
• Programmable Clock-output
13.1 Auto-reload Mode
The Auto-reload mode configures Timer 2 as a 16-bit timer or event counter with automatic
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 13-1. 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 under-
flow 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.