AT89S8252
Auto-Reload (Up or Down Counter) (Continued)
A logic 0 at T2EX makes Timer 2 count down. The timer
underflows when TH2 and TL2 equal the values stored in
RCAP2H and RCAP2L. The underflow sets the TF2 bit
and causes 0FFFFH to be reloaded into the timer regis-
ters.
The EXF2 bit toggles whenever Timer 2 overflows or un-
derflows and can be used as a 17th bit of resolution. In this
operating mode, EXF2 does not flag an interrupt.
Figure 2. Timer 2 Auto Reload Mode (DCEN = 0)
Table 9. T2MOD—Timer 2 Mode Control Register
T2MOD Address = 0C9H
Reset Value = XXXX XX00B
Not Bit Addressable
—
—
—
—
—
—
T2OE
DCEN
Bit 7
6
5
4
3
2
1
0
Symbol
—
T2OE
DCEN
Function
Not implemented, reserved for future use.
Timer 2 Output Enable bit.
When set, this bit allows Timer 2 to be configured as an up/down counter.
11