at90ls8535-8mi ATMEL Corporation, at90ls8535-8mi Datasheet - Page 38

• Manufacturer Part Number: at90ls8535-8mi
• Description: 8-bit Microcontroller With 8k Bytes In-system Programmable Flash
• Manufacturer: ATMEL Corporation

Timer/Counter1 – TCNT1H
AND TCNT1L
38
AT90S/LS8535
• Bit 3 – CTC1: Clear Timer/Counter1 on Compare Match
When the CTC1 control bit is set (one), the Timer/Counter1 is reset to $0000 in the clock
cycle after a compareA match. If the CTC1 control bit is cleared, Timer/Counter1 contin-
ues counting and is unaffected by a compare match. Since the compare match is
detected in the CPU clock cycle following the match, this function will behave differently
when a prescaling higher than 1 is used for the timer. When a prescaling of 1 is used
and the compareA register is set to C, the timer will count as follows if CTC1 is set:
... | C-2 | C-1 | C | 0 | 1 |...
When the prescaler is set to divide by 8, the timer will count like this:
... | C-2, C-2, C-2, C-2, C-2, C-2, C-2, C-2 | C-1, C-1, C-1, C-1, C-1, C-1, C-1, C-1 | C, 0,
0, 0, 0, 0, 0, 0 |1,1,1,1,1,1,1,1|...
In PWM mode, this bit has no effect.
• Bits 2, 1, 0 – CS12, CS11, CS10: Clock Select1, Bits 2, 1 and 0
The Clock Select1 bits 2, 1 and 0 define the prescaling source of Timer/Counter1.
Table 13. Clock 1 Prescale Select
The Stop condition provides a Timer Enable/Disable function. The CK down divided
modes are scaled directly from the CK oscillator clock. If the external pin modes are
used, the corresponding setup must be performed in the actual Direction Control Regis-
ter (cleared to zero gives an input pin).
This 16-bit register contains the prescaled value of the 16-bit Timer/Counter1. To
ensure that both the high and low bytes are read and written simultaneously when the
CPU accesses these registers, the access is performed using an 8-bit temporary regis-
ter (TEMP). This temporary register is also used when accessing OCR1A, OCR1B and
ICR1. If the main program and also interrupt routines perform access to registers using
Bit
$2D ($4D)
$2C ($4C)
Read/Write
Initial Value
CS12
0
0
0
0
1
1
1
1
MSB
R/W
R/W
15
7
0
0
CS11
0
0
1
1
0
0
1
1
R/W
R/W
14
6
0
0
CS10
0
1
0
1
0
1
0
1
R/W
R/W
13
5
0
0
Stop, the Timer/Counter1 is stopped.
CK
CK/8
CK/64
CK/256
CK/1024
External Pin T1, falling edge
External Pin T1, rising edge
Description
R/W
R/W
12
4
0
0
R/W
R/W
11
3
0
0
R/W
R/W
10
2
0
0
R/W
R/W
9
1
0
0
LSB
R/W
R/W
8
0
0
0
1041H–11/01
TCNT1H
TCNT1L