The PIC16F84A is an 18-pin DIP IC with the pin-out shown in Figure 1. It has external power and ground pins (VDD and VSS), 13 binary input/output (I/O) pins (RA [0-4] and RB [0-7]), and uses an external clock signal (OSC1 and OSC2).
The master clear (MCLR) pin is active low, meaning the PIC is reset when the pin is grounded. MCLR must be held high during PIC operation. The power supply voltage (5 Vdc) and ground are connected to pins labeled VDD and VSS (pins 14 and 5), respectively. Pin 4 (MCLR) is attached to 5 Vdc with a 4.7 KΩ resistor to ensure continuous operation.
PIC16F84A (Click to enlarge)
If this pin were left unconnected (floating),the PIC could spontaneously reset itself. An accurate clock frequency can be obtained by connecting a 4MHz crystal (sometimes indicated as XT) across pins 15 and 16 which are also connected to ground through 22 pF capacitors.
The pins labeled RAx and RBx provide binary I/O. They are divided into two groups called PORTs. PORTA refers to pins RA0 through RA4 and PORTB refers to pins through RB0 through RB7. PORTA and PORTB are compiler variable names that provide access to registers on the PIC.
Each bit within the PORT can be referred to individually by its bit location (e.g., PORTA.3 refers to bit 3 in the PORTA register).
s: coreelectronics.info
