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ST72321 Datasheet(PDF) 73 Page - STMicroelectronics |
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ST72321 Datasheet(HTML) 73 Page - STMicroelectronics |
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73 / 185 page  ST72321 73/185 16-BIT TIMER (Cont’d) 10.4.3.3 Input Capture In this section, the index, i, may be 1 or 2 because there are 2 input capture functions in the 16-bit timer. The two 16-bit input capture registers (IC1R and IC2R) are used to latch the value of the free run- ning counter after a transition is detected on the ICAP i pin (see figure 5). IC iR register is a read-only register. The active transition is software programmable through the IEDG i bit of Control Registers (CRi). Timing resolution is one count of the free running counter: ( fCPU/CC[1:0]). Procedure: To use the input capture function select the follow- ing in the CR2 register: – Select the timer clock (CC[1:0]) (see Table 16 Clock Control Bits). – Select the edge of the active transition on the ICAP2 pin with the IEDG2 bit (the ICAP2 pin must be configured as floating input or input with pull-up without interrupt if this configuration is available). And select the following in the CR1 register: – Set the ICIE bit to generate an interrupt after an input capture coming from either the ICAP1 pin or the ICAP2 pin – Select the edge of the active transition on the ICAP1 pin with the IEDG1 bit (the ICAP1pin must be configured as floating input or input with pull- up without interrupt if this configuration is availa- ble). When an input capture occurs: – ICF i bit is set. – The IC iR register contains the value of the free running counter on the active transition on the ICAP i pin (see Figure 47). – A timer interrupt is generated if the ICIE bit is set and the I bit is cleared in the CC register. Other- wise, the interrupt remains pending until both conditions become true. Clearing the Input Capture interrupt request (i.e. clearing the ICF i bit) is done in two steps: 1. Reading the SR register while the ICF i bit is set. 2. An access (read or write) to the IC iLR register. Notes: 1. After reading the IC iHR register, transfer of input capture data is inhibited and ICF i will never be set until the IC iLR register is also read. 2. The IC iR register contains the free running counter value which corresponds to the most recent input capture. 3. The 2 input capture functions can be used together even if the timer also uses the 2 output compare functions. 4. In One pulse Mode and PWM mode only Input Capture 2 can be used. 5. The alternate inputs (ICAP1 & ICAP2) are always directly connected to the timer. So any transitions on these pins activates the input capture function. Moreover if one of the ICAP i pins is configured as an input and the second one as an output, an interrupt can be generated if the user tog- gles the output pin and if the ICIE bit is set. This can be avoided if the input capture func- tion i is disabled by reading the ICiHR (see note 1). 6. The TOF bit can be used with interrupt genera- tion in order to measure events that go beyond the timer range (FFFFh). MS Byte LS Byte ICiR IC iHR IC iLR |
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