PIC18LF4331-ESLASHML datasheet(168/392 Pages) MICROCHIP

168 / 392 page

PIC18F2331/2431/4331/4431

DS39616D-page 168

 2010 Microchip Technology Inc.

FIGURE 17-13:

VELOCITY MEASUREMENT TIMING(1)

17.2.6.2

Velocity Postscaler

The velocity event pulse (velcap, see Figure 17-12)

serves as the TMR5 capture trigger to IC1 while in the

Velocity mode. The number of velocity events are

reduced by the velocity postscaler before they are used

as the input capture clock. The velocity event reduction

ratio can be set with the PDEC<1:0> control bits

(QEICON<1:0>) to 1:4, 1:16, 1:64 or no reduction (1:1).

The velocity postscaler settings are automatically

reloaded from their previous values as the Velocity

mode is re-enabled.

17.2.6.3

CAP1REN in Velocity Mode

The TMR5 value can be reset (TMR5 register

pair = 0000h) on a velocity event capture by setting

the CAP1REN bit (CAP1CON<6>). When CAP1REN

is cleared, the TMR5 time base will not be reset on

any velocity event capture pulse. The VELR register

pair, however, will continue to be updated with the

current TMR5 value.

QEB

QEA

cnt_reset(3)

TMR5(2)

velcap

BCF T5CON, VELM

VELR(2)

1529

1537

vel_out

Old Value

Forward

IC1IF(4)

Instr.

Execution

MOVWF QEICON(5)

BCF PIE2, IC1IE

BSF PIE2, IC1IE

CAP1REN

Note 1:

Timing shown is for QEIM<2:0> = 101, 110 or 111 (x4 Update mode enabled) and the velocity postscaler divide ratio

is set to divide-by-4 (PDEC<1:0> = 01).

The VELR register latches the TMR5 count on the “velcap” capture pulse. Timer5 must be set to the Synchronous Timer

or Counter mode. In this example, it is set to the Synchronous Timer mode, where the TMR5 prescaler divide ratio = 1

(i.e., Timer5 Clock = TCY).

The TMR5 counter is reset on the next Q1 clock cycle following the “velcap” pulse. The TMR5 value is unaffected

when the Velocity Measurement mode is first enabled (VELM = 0). The velocity postscaler values must be

reconfigured to their previous settings when re-entering Velocity Measurement mode. While making speed

measurements of very slow rotational speeds (e.g., servo-controller applications), the Velocity Measurement mode

may not provide sufficient precision. The Pulse-Width Measurement mode may have to be used to provide the

additional precision. In this case, the input pulse is measured on the CAP1 input pin.

IC1IF interrupt is enabled by setting IC1IE as follows: BSF PIE2, IC1IE. Assume IC1E bit is placed in the PIE2

(Peripheral Interrupt Enable 2) register in the target device. The actual IC1IF bit is written on the Q2 rising edge.

The post decimation value is changed from PDEC = 01 (decimate by 4) to PDEC = 00 (decimate by 1).

Reverse

PIC18LF4331-E/ML Datasheet(PDF) 168 Page - Microchip Technology

PIC18LF4331-E/ML Datasheet(HTML) 168 Page - Microchip Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 ...More

Datasheet Download

Link URL