ata6616 ATMEL Corporation, ata6616 Datasheet - Page 112

• Manufacturer Part Number: ata6616
• Description: Microcontroller With Lin Transceiver, 5v Regulator And Watchdog
• Manufacturer: ATMEL Corporation

4.11.2.1
4.11.3
4.11.4
112
ATA6616/ATA6617 [Preliminary]
Timer/Counter Clock Sources
Counter Unit
Definitions
The following definitions are used extensively throughout the section:
The Timer/Counter can be clocked by an internal synchronous or an external asynchronous
clock source. The clock source is selected by the clock select logic which is controlled by the
clock select (CS02:0) bits located in the Timer/Counter control register (TCCR0).The clock
source clk
is written to logic one, the clock source is taken from the Timer/Counter Oscillator connected to
XTAL1 and XTAL2 or directly from XTAL1. For details on asynchronous operation, see
chronous Status Register – ASSR” on page
“Timer/Counter0 Prescaler” on page
The main part of the 8-bit Timer/Counter is the programmable bi-directional counter unit.
4-31
Figure 4-31. Counter Unit Block Diagram
Signal description (internal signals):
BOTTOM
MAX
TOP
shows a block diagram of the counter and its surrounding environment.
count
direction
clear
clk
top
bottom
T0
T0
DATA BUS
is by default equal to the MCU clock, clk
TCNTn
The counter reaches the BOTTOM when it becomes zero (0x00).
The counter reaches its MAXimum when it becomes 0xFF (decimal 255).
The counter reaches the TOP when it becomes equal to the highest value in the count
sequence. The TOP value can be assigned to be the fixed value 0xFF (MAX) or the value
stored in the OCR0A Register. The assignment is dependent on the mode of operation.
Increment or decrement TCNT0 by 1.
Selects between increment and decrement.
Clear TCNT0 (set all bits to zero).
Timer/Counter0 clock.
Signalizes that TCNT0 has reached maximum value.
Signalizes that TCNT0 has reached minimum value (zero).
direction
count
clear
bottom
123.
Control Logic
127. For details on clock sources and prescaler, see
top
TOVn
(Int.Req.)
DRAFT
clk
Tn
I/O
Prescaler
. When the AS0 bit in the ASSR Register
clk
TnS
Oscillator
9132A–AUTO–10/08
clk I/O
XTAL2
XTAL1
“Asyn-
Figure