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THROUGH THE LOOKING GLASS

Taking a Look at the PIC18Cxxx Series
by David Brobst

Start ý PIC18Cxxx Chips ý Memory ý Data Memory ý Advanced Indirect Addressing ý Deep and Accessible Stack ý Interrupts ý Power-On Features ý Clock Speed ý 10-Bit A/D ý Hardware Multiplier ý Timers ý CCP/PWM ý USART ý I²C Master ý Table Read/Write ý Current Status ý Sources and PDF

USART

The PIC18Cxxx family contains a full function USART, much like the mid-range PIC devices, with an additional feature. The PIC18Cxxx USART allows 9-bit transmission and reception, with the ninth bit (MSB) acting as an address signifier. With this configuration, the USART in the PIC18Cxxx can be set up to generate an interrupt only when it receives a byte with the ninth bit set. If the ninth bit is set, the program can look at the byte and see if the eight LSBs match the address of the PIC18Cxxx chip.

In a multi-drop system (many devices sharing the same serial line), this addressing scheme is a great first step to increasing the throughput and reliability of the communication channel. Listing 1 shows an assembly code fragment that demonstrates addressing setup and use in the PIC18Cxxx.

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