Rainbow Electronics AT90LS8535 - Manual (Page 37)

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AT90S/LS8535
1041H–11/01
Note: X = A or B.
In PWM mode, these bits have a different function. Refer to Table 15 for a detailed
description. When changing the COM1X1/COM1X0 bits, Output Compare Interrupt 1
must be disabled by clearing their Interrupt Enable bits in the TIMSK Register. Other-
wise an interrupt can occur when the bits are changed.
• Bits 3..2 – Res: Reserved Bits
These bits are reserved bits in the AT90S8535 and always read zero.
• Bits 1..0 – PWM11, PWM10: Pulse Width Modulator Select Bits
These bits select PWM operation of Timer/Counter1 as specified in Table 12. This mode
is described on page 40.
Timer/Counter1 Control
Register B – TCCR1B
• Bit 7 – ICNC1: Input Capture1 Noise Canceler (4 CKs)
When the ICNC1 bit is cleared (zero), the Input Capture Trigger Noise Canceler function
is disabled. The input capture is triggered at the first rising/falling edge sampled on the
ICP (input capture pin) as specified. When the ICNC1 bit is set (one), four successive
samples are measured on the ICP (input capture pin), and all samples must be high/low
according to the input capture trigger specification in the ICES1 bit. The actual sampling
frequency is XTAL clock frequency.
• Bit 6 – ICES1: Input Capture1 Edge Select
While the ICES1 bit is cleared (zero), the Timer/Counter1 contents are transferred to the
Input Capture Register (ICR1) on the falling edge of the input capture pin (ICP). While
the ICES1 bit is set (one), the Timer/Counter1 contents are transferred to the Input Cap-
ture Register (ICR1) on the rising edge of the input capture pin (ICP).
• Bits 5, 4 – Res: Reserved Bits
These bits are reserved bits in the AT90S8535 and always read zero.
Table 11. Compare 1 Mode Select
COM1X1 COM1X0 Description
0 0 Timer/Counter1 disconnected from output pin OC1X
0 1 Toggle the OC1X output line.
1 0 Clear the OC1X output line (to zero).
1 1 Set the OC1X output line (to one).
Table 12. PWM Mode Select
PWM11 PWM10 Description
0 0 PWM operation of Timer/Counter1 is disabled
0 1 Timer/Counter1 is an 8-bit PWM
1 0 Timer/Counter1 is a 9-bit PWM
1 1 Timer/Counter1 is a 10-bit PWM
Bit 7 6 5 4 3 2 1 0
$2E ($4E) ICNC1 ICES1 – – CTC1 CS12 CS11 CS10 TCCR1B
Read/Write R/W R/W R R R/W R/W R/W R/W
Initial Value 0 0 0 0 0 0 0 0