Panel Meter Interface
Components
1mA Full scale meter
94 Ohms coil resistance
5K Ohm resistor @ 5V = 1mA
MCP4821
| Pin No. | Symbol | Function |
|---|---|---|
| 1 | Vdd | Supply (2.7 to 5.5V) |
| 2 | CS | Chip Select |
| 3 | SCK | Serial Clock Input |
| 4 | SDI | Serial Data Input |
| 5 | LDAC | Sync input |
| 6 | SHDN | Hardware shutdown |
| 7 | AVss | Analog ground |
| 8 | VoutA | DACa Output |
PIC Assembly Code
SPIclk macro BSF PORTC,SCK BCF PORTC,SCK endm ;Setup direction BCF TRISB,RB1 ; RB1 as Output BCF TRISC,SCL ; SDO as Output BCF TRISC,SDA ; SCK as Output ;Set initial pin states BSF PORTB,RB1 ;Chip Select, active low BCF PORTC,SCK BCF PORTC,SDO myloop movlw 0xF0 movwf DAC,A movlw 0x00 movwf DAC+1,A CALL SPIclkout CALL Delay goto myloop ; ================= ; === Functions === ; ================= SPIclkout BCF PORTB,RB1 ; Clear CS (Active low) BCF PORTC,SDO ; 0 SPIclk SPIclk SPIclk BSF PORTC,SDO ; 1 SPIclk MOVLW 0x08 MOVWF Temp,A SPIloop BTFSS DAC,7 BCF PORTC,SDO ; 0 BTFSC DAC,7 BSF PORTC,SDO ; 1 SPIclk RLNCF DAC,F,A DECFSZ Temp,F,A goto SPIloop MOVLW 0x04 SPIloop2 BTFSS DAC+1,7 BCF PORTC,SDO ; 0 BTFSC DAC+1,7 BSF PORTC,SDO ; 1 SPIclk RLNCF DAC+1,F,A DECFSZ Temp,F,A goto SPIloop2 RLNCF DAC+1,F,A RLNCF DAC+1,F,A RLNCF DAC+1,F,A RLNCF DAC+1,F,A BSF PORTB,RB1 ; Set CS high return