PIC18F2331 Datasheet, PDF (177/396 Pages) Microchip Technology – 28/40/44-Pin Enhanced Flash Microcontrollers with nanoWatt Technology, High Performance PWM and A/D

PIC18F2331/2431/4331/4431
FIGURE 16-11:
QEA
QEB
QEI MODULE RESET TIMING WITH THE INDEX INPUT
Forward
Reverse
Note 2
Note 2
count (+/-)
POSCNT⁽¹⁾
+1 +1 +1 +1 +1 +1 +1 +1 +1 +1 +1 +1
-1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1 -1
MAXCNT
MAXCNT=1527
INDX
IC2QEIF
UP/DOWN
Note 6
Position
counter load
Q4⁽³⁾
Q1⁽⁴⁾
Q4⁽³⁾
Q1⁽⁵⁾
Note 1: POSCNT register is shown in QEI x4 Update mode (POSCNT increments on every rising and every falling edge of
QEA and QEB input signals)
2: When INDX Reset pulse is detected, POSCNT is reset to ‘0’ on the next QEA or QEB edge. POSCNT is set to
MAXCNT when POSCNT = 0 (when decrementing), which occurs on the next QEA or QEB edge. Similar Reset
sequence occurs for the reverse direction except that the INDX signal is recognized on its falling edge. The Reset
is generated on the next QEA or QEB edge.
3: IC2QEI is enabled for one TCY clock cycle.
4: Position counter is loaded with ‘0000h’ (i.e., Reset) on the next QEA or QEB edge when INDX is high.
5: Position counter is loaded with MAXCNT value (e.g., 1527h) on the next QEA or QEB edge following the INDX
falling edge input signal detect).
6: IC2QEIF must be cleared in software.
16.2.6 VELOCITY MEASUREMENT
The velocity pulse generator, in conjunction with the
IC1 and the synchronous TMR5 (in synchronous
operation), provides a method for high accuracy speed
measurements at both low and high mechanical motor
speeds. The Velocity mode is enabled when the VELM
bit is cleared (= 0) and QEI is set to one of its operating
modes (see Table 16-6).
To optimize register space, the input capture channel
one (IC1) is used to capture TMR5 counter values.
Input capture buffer register, CAP1BUF, is redefined in
Velocity Measurement mode, VELM = 0, as the
Velocity Register buffer (VREGH, VREGL).
TABLE 16-6: VELOCITY PULSES
QEIM<2:0>
Velocity Event Mode
001 x2 Velocity Event mode. The velocity
010 pulse is generated on every QEA
edge.
101 x4 Velocity Event mode. The velocity
110 pulse is generated on every QEA and
QEB active edge.
 2003 Microchip Technology Inc.
Preliminary
DS39616B-page 175