at90ls8535-8mi ATMEL Corporation, at90ls8535-8mi Datasheet - Page 46

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

Asynchronous Status
Register – ASSR
46
AT90S/LS8535
Table 20. PWM Outputs OCR2 = $00 or $FF
In PWM mode, the Timer Overflow Flag (TOV2) is set when the counter advances from
$00. Timer Overflow Interrupt2 operates exactly as in normal Timer/Counter mode, i.e.,
it is executed when TOV2 is set, provided that Timer Overflow Interrupt and global inter-
rupts are enabled. This also applies to the Timer Output Compare flag and interrupt.
The frequency of the PWM will be Timer Clock Frequency divided by 510.
• Bit 7..4 – Res: Reserved Bits
These bits are reserved bits in the AT90S8535 and always read as zero.
• Bit 3 – AS2: Asynchronous Timer/Counter2
When AS2 is set (one), Timer/Counter2 is clocked from the TOSC1 pin. Pins PC6 and
PC7 become connected to a crystal oscillator and cannot be used as general I/O pins.
When cleared (zero), Timer/Counter2 is clocked from the internal system clock, CK.
When the value of this bit is changed, the contents of TCNT2, OCR2 and TCCR2 might
get corrupted.
• Bit 2 – TCN2UB: Timer/Counter2 Update Busy
When Timer/Counter2 operates asynchronously and TCNT2 is written, this bit becomes
set (one). When TCNT2 has been updated from the temporary storage register, this bit
is cleared (zero) by hardware. A logical “0” in this bit indicates that TCNT2 is ready to be
updated with a new value.
• Bit 1 – OCR2UB: Output Compare Register2 Update Busy
When Timer/Counter2 operates asynchronously and OCR2 is written, this bit becomes
set (one). When OCR2 has been updated from the temporary storage register, this bit is
cleared (zero) by hardware. A logical “0” in this bit indicates that OCR2 is ready to be
updated with a new value.
• Bit 0 – TCR2UB: Timer/Counter Control Register2 Update Busy
When Timer/Counter2 operates asynchronously and TCCR2 is written, this bit becomes
set (one). When TCCR2 has been updated from the temporary storage register, this bit
is cleared (zero) by hardware. A logical “0” in this bit indicates that TCCR2 is ready to be
updated with a new value.
If a write is performed to any of the three Timer/Counter2 registers while its Update Busy
flag is set (one), the updated value might get corrupted and cause an unintentional inter-
rupt to occur.
The mechanisms for reading TCNT2, OCR2 and TCCR2 are different. When reading
TCNT2, the actual timer value is read. When reading OCR2 or TCCR2, the value in the
temporary storage register is read.
Bit
$22 ($22)
Read/Write
Initial Value
COM21
1
1
1
R
7
–
0
R
6
–
0
COM20
0
1
1
R
5
–
0
4
–
R
0
OCR2
AS2
R/W
$FF
$FF
$00
3
0
TCN2UB
R
2
0
OCR2UB
R
1
0
Output PWM2
TCR2UB
H
H
L
R
0
0
1041H–11/01
ASSR