AT89LP428-20MU ATMEL [ATMEL Corporation], AT89LP428-20MU Datasheet - Page 66

• Manufacturer Part Number: AT89LP428-20MU
• Description: 8-bit Microcontroller with 4K/8K Bytes In-System Programmable Flash
• Manufacturer: ATMEL [ATMEL Corporation]

13.2.1
13.3
66
Output Compare Mode
AT89LP428/828
Timer 2 Operation for Capture Mode
Each CCA channel has an associated external capture input pin: CCA (P2.0), CCB (P2.1), CCC
(P2.2) and CCD (P2.3). External capture events are always edge-triggered and can be selected
to occur at a negative edge, positive edge, or both (toggle). Capture inputs are sampled every
clock cycle and a new value must be held for at least 2 clock cycles to be correctly sampled by
the device. The maximum achievable capture rate will be determined by how fast the software
can retrieve the captured data. There is no protection against capture events overrunning the
data register.
Capture events may also be triggered internally by the overflows of Timer 0 or Timer 1, or by an
event from the dual analog comparators. Any comparator event which can generate a compara-
tor interrupt may also be used as a capture event. However, Timer 2 should not be selected as
the comparator clock source when using the comparator as the capture trigger.
Capture channels are intended to work with Timer 2 in capture mode CP/RL2 = 1. Captures can
still occur when Timer 2 operates in other modes; however, the full 16-bit count range may not
be available. The TF2 flag can be used to determine if the timer overflowed before the capture
occurred. If the timer is operating in dual-slope mode (CP/RL2 = 0, T2CM
direction (Up = 0 and Down = 1) at the time of the event will be captured into the channel’s
CDIRx bit in CCCx. CTCx must be cleared to 0 for all channels if Timer 2 is operating in Baud
Rate mode or errors may occur in the serial communication.
The Compare/Capture Array provides a variety of compare modes suitable for event timing or
waveform generation. The CCA channels are configured for compare mode by setting the CCMx
bit in the associated CCCx register to 1. A compare event occurs when the 16-bit contents of a
channel’s data register match the contents of Timer 2 (TH2 and TL2). The compare event also
sets the channel’s interrupt flag CCFx in T2CCF and may optionally clear Timer 2 to 0000H if the
CTCx bit in CCCx is set. A diagram of a CCA channel in compare mode is shown in
Figure 13-3. CCA Compare Mode Diagram
T2CCL
CCxL
00H
TL2
Shadow
T2CCH
CCxH
00H
TH2
=
T2CCC
CCCx
CTCx
CCFx
CxM
2-0
CIENx
1-0
Interrupt
= 1xB), the count
CCx (P2.x)
3654A–MICRO–8/09
Figure
13-3.