SN8F2250B Series
USB 2.0 Full-Speed 8-Bit Micro-Controller
8.4.4 TC0R AUTO-LOAD REGISTER
TC0 timer is with auto-load function controlled by ALOAD0 bit of TC0M. When TC0C overflow occurring, TC0R value
will load to TC0C by system. It is easy to generate an accurate time, and users don’t reset TC0C during interrupt
service routine.
TC0 is double buffer design. If new TC0R value is set by program, the new value is stored in 1st buffer. Until TC0
overflow occurs, the new value moves to real TC0R buffer. This way can avoid TC0 interval time error and glitch in
PWM and Buzzer output.
Note: Under PWM mode, auto-load is enabled automatically. The ALOAD0 bit is selecting overflow
boundary.
08AH
TC0R
Read/Write
After reset
Bit 7
TC0R7
W
Bit 6
TC0R6
W
Bit 5
TC0R5
W
Bit 4
TC0R4
W
Bit 3
TC0R3
W
Bit 2
TC0R2
W
Bit 1
TC0R1
W
Bit 0
TC0R0
W
0
0
0
0
0
0
0
0
The equation of TC0R initial value is as following.
TC0R initial value = N - (TC0 interrupt interval time * input clock)
N is TC0 overflow boundary number. TC0 timer overflow time has six types (TC0 timer, TC0 event counter, TC0 Fcpu
clock source, TC0 Fosc clock source, PWM mode and no PWM mode). These parameters decide TC0 overflow time
and valid value as follow table.
TC0R valid
value
TC0R value
binary type
TC0CKS PWM0 ALOAD0 TC0OUT
N
0
1
1
1
1
-
x
0
0
1
1
-
x
0
1
0
1
-
256
256
64
32
16
0x00~0xFF 00000000b~11111111b
0x00~0xFF 00000000b~11111111b
0
1
0x00~0x3F
0x00~0x1F
0x00~0x0F
xx000000b~xx111111b
xxx00000b~xxx11111b
xxxx0000b~xxxx1111b
256
0x00~0xFF 00000000b~11111111b
¾
Example: To set 1ms interval time for TC0 interrupt. TC0 clock source is Fcpu (TC0KS=0) and no PWM
output (PWM0=0). High clock is internal 6MHz. Fcpu=Fosc/1. Select TC0RATE=010 (Fcpu/64).
TC0R initial value = N - (TC0 interrupt interval time * input clock)
= 256 - (1ms * 6MHz / 1 / 64)
= 256 - (10-3 * 6 * 106 / 1 / 64)
= 162
= A2H
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