General-purpose timers (TIM2/TIM3/TIM4/TIM5) RM0440
1288/2126 RM0440 Rev 4
Index management in non-quadrature mode
The Figure 422 and Figure 423 below detail how the index is managed in directional clock
mode and clock plus direction mode, when the SMS[3:0] bitfield is equal to 1010, 1011,
1100, 1101.
For both of these modes, the index sensitivity is set with the IPOS[0] bit as following:
• IPOS[0] = 0: Index is detected on clock low level
• IPOS[0] = 1: Index is detected on clock high level
The IPOS[1] bit is not-significant.
Figure 422. Index behavior in clock + direction mode, IPOS[0] = 1
Figure 423. Index behavior in directional clock mode, IPOS[0] = 1
Encoder error management
For encoder configurations where 2 quadrature signals are available, it is possible to detect
transition errors. The reading on the 2 inputs corresponds to a 2-bit gray code which can be
represented as a state diagram, on the Figure 424. below. A single bit is expected to change
at once. An erroneous transition will set the TERRF interrupt flag in the TIMx_SR status
MSv45777V1
Direction (TI1)
Clock (TI2)
Index
Counter x2 mode
Counter x1 mode
321 34 72 6 5
2 1
7
1
7 0
7 0
MSv45778V1
DIR bit
Counter x2 mode
Counter x1 mode
321 34 12 0 8
2 1
9
1
9 0
0
9
0
9
Clock Down (TI1)
Clock Up (TI2)
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