AT89LP428-20MU ATMEL [ATMEL Corporation], AT89LP428-20MU Datasheet - Page 52

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

12. Enhanced Timer 2
52
AT89LP428/828
The AT89LP428/828 includes a 16-bit Timer/Counter 2 with the following features:
Timer 2 is a 16-bit Timer/Counter that can operate as either a timer or an event counter. The
type of operation is selected by bit C/T2 in the SFR T2CON. Timer 2 has three operating modes:
capture, auto-reload (up or down counting), and baud rate generator. The modes are selected
by bits in T2CON and T2MOD, as shown in
the Compare/Capture Array (see
Timer 2 consists of two 8-bit registers, TH2 and TL2. In the Timer function, the register is incre-
mented every clock cycle. Since a clock cycle consists of one oscillator period, the count rate is
equal to the oscillator frequency. The timer rate can be prescaled by a value between 1 and 16
using the Timer Prescaler (see
In the Counter function, the register is incremented in response to a 1-to-0 transition at its corre-
sponding external input pin, T2. In this function, the external input is sampled every clock cycle.
When the samples show a high in one cycle and a low in the next cycle, the count is incre-
mented. The new count value appears in the register during the cycle following the one in which
the transition was detected. Since two clock cycles are required to recognize a 1-to-0 transition,
the maximum count rate is 1/2 of the oscillator frequency. To ensure that a given level is sam-
pled at least once before it changes, the level should be held for at least one full clock cycle.
Table 12-1.
The following definitions for Timer 2 are used in the subsequent paragraphs:
Table 12-2.
RCLK + TCLK
• 16-bit timer/counter with one 16-bit reload/capture register
• One external reload/capture input
• Up/Down counting mode with external direction control
• UART baud rate generation
• Output-pin toggle on timer overflow
• Dual slope symmetric operating modes
BOTTOM
Symbol
MAX
TOP
MIN
0
0
0
1
X
X
Timer 2 Operating Modes
Timer 2 Definitions
Definition
0000H
FFFFH
16-bit value of {RCAP2H,RCAP2L} (standard modes)
16-bit value of {RCAP2H,RCAP2L} (enhanced modes)
CP/RL2
X
X
X
0
0
1
DCEN
0
1
X
X
X
X
Table 6-2 on page
“Compare/Capture Array” on page
T2OE
X
X
0
0
0
1
Table
12-3. Timer 2 also serves as the time base for
TR2
23).
1
1
1
1
1
0
Mode
16-bit Auto-reload
16-bit Auto-reload Up-down
16-bit Capture
Baud Rate Generator
Frequency Generator
(Off)
61).
3654A–MICRO–8/09