DSPIC30F4012-20I/SO Microchip Technology, DSPIC30F4012-20I/SO Datasheet - Page 9

• Manufacturer Part Number: DSPIC30F4012-20I/SO
• Description: IC, DSC, 16BIT, 48KB 20MHZ, 5.5V, SOIC28
• Manufacturer: Microchip Technology
• Series: DsPIC30Fr

Specifications of DSPIC30F4012-20I/SO

• Core Frequency: 20MHz
• Embedded Interface Type: CAN, I2C, SPI, UART
• No. Of I/o's: 20
• Flash Memory Size: 48KB
• Supply Voltage Range: 2.5V To 5.5V
• Core Processor: dsPIC
• Core Size: 16-Bit
• Speed: 20 MIPS
• Connectivity: CAN, I²C, SPI, UART/USART
• Peripherals: Brown-out Detect/Reset, Motor Control PWM, QEI, POR, PWM, WDT
• Number Of I /o: 20
• Program Memory Size: 48KB (16K x 24)
• Program Memory Type: FLASH
• Eeprom Size: 1K x 8
• Ram Size: 2K x 8
• Voltage - Supply (vcc/vdd): 2.5 V ~ 5.5 V
• Data Converters: A/D 6x10b
• Oscillator Type: Internal
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 28-SOIC (7.5mm Width)
• Package: 28SOIC W
• Device Core: dsPIC
• Family Name: dsPIC30
• Maximum Speed: 20 MHz
• Operating Supply Voltage: 2.5|3.3|5 V
• Data Bus Width: 16 Bit
• Number Of Programmable I/os: 20
• Interface Type: CAN/I2C/SPI/UART
• On-chip Adc: 6-chx10-bit
• Number Of Timers: 5
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• For Use With: XLT28SO-1 - SOCKET TRANSITION 28SOIC 300MIL
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant, Lead free / RoHS Compliant
• Other names: DSPIC30F401220ISO

14. Module: QEI Interrupt Generation
EXAMPLE 8:
© 2008 Microchip Technology Inc.
unsigned int POSCNT_b15 = 0;
unsigned int Motor_Position = 0;
int main(void)
{
}
void __attribute__((__interrupt__)) _QEIInterrupt(void)
{
}
The Quadrature Encoder Interface (QEI) module
does not generate an interrupt when MAXCNT is
set to 0xFFFF and the following events occur:
1. POSCNT underflows from 0x0000 to 0xFFFF.
2. POSCNT stops.
3. POSCNT overflows from 0xFFFF to 0x0000.
This sequence of events occurs when the motor is
running in one direction, which causes POSCNT to
underflow to 0xFFFF. Once this happens, the
motor stops and starts to run in the opposite
direction, which generates an overflow from
0xFFFF to 0x0000. The QEI module does not
generate an interrupt when this condition occurs.
// ... User's code
MAXCNT = 0x7FFF;
Motor_Position = POSCNT_b15 + POSCNT;
// ... User's code
IFSxbits.QEIIF = 0;
POSCNT_b15 ^= 0x8000; // Overflow or Underflow
// Instead of 0xFFFF
// Clear QEI interrupt flag
// x=2 for dsPIC30F
// x=3 for dsPIC33F
dsPIC30F4011/4012
Work around
To prevent this condition from occurring, set
MAXCNT to 0x7FFF, which will cause an interrupt
to be generated by the QEI module.
In addition, a global variable could be used to keep
track of bit 15, so that when an overflow or
underflow condition is present on POSCNT, the
variable will toggle bit 15. Example 8 shows the
code required for this global variable.
DS80215K-page 9