Nuts and Volts - March 2015

#FUSES RTCOSC_T1
 //RTCC uses Secondary Oscillator as reference
 //source
#FUSES NODSBOR
 //BOR disabled in Deep Sleep
#FUSES NODSWDT
 //Deep Sleep Watchdog Timer disabled
#FUSES DSWDT2147483648
 //DSWDT uses 1:2147483648 Postscale
#FUSES IOL1WAY
 //Allows only one reconfiguration of
 //peripheral pins
#FUSES ADC10
 //ADC is 10-bits
#FUSES MSSPMSK7
 //MSSP uses 7 bit Masking mode
#FUSES WPFP
 //Write/Erase Protect Page Start/End Location
#FUSES NOWPCFG
 //Configuration Words page is not
 //erase/write-protected
#FUSES WPDIS
 //All Flash memory may be erased or written
#FUSES WPEND
 //Flash pages WPFP to Configuration Words
 //page protected

PmodUSBUART combination to a PC USB port and kick off your favorite terminal emulator. I’ve provided the C source code for download at the article link, so all you have to do is compile the code and load it into your version of the PIC18F27J13-based hardware described in this text.

Connecting to the Moray

You can download the Moray schematic from the Ackme website (https://ack.me). You will see that all you really have to do is bypass the Moray’s USB portal. You can power the Moray with an external + 5 volt power supply if you decide to tap in before the Moray’s onboard voltage regulator. You will only need a + 3. 3 volt supply if you bypass the regulator all together. The Moray’s UART Rx and Tx signals are available at the Moray’s male I/O header.

#device ICD=TRUE
#use delay(internal=8000000)
#use FIXED_IO( A_outputs=PIN_A2 )
#define user_led PIN_A2

The Moray technical documentation describes in detail the commands and responses that pass over the serial connection. You can emulate the sequences by sending them to the PIC18F27J13 using the terminal emulator. The CCS C compiler IDE debugger allows you to peek into the PIC18F27J13’s EUSART receive ring buffer and examine the Moray’s responses.

#use rs232(baud=115200,parity=N,xmit=PIN_C6,rcv=
PIN_C7,bits=8,stream=MORAY)

Thanks to the CCS compiler and a PIC18F27J13, you can now add embedded Wi-Fi to your Design Cycle. NV

Following the inclusion of the PIC hardware definition file 18F27J13.h, all of the fuse settings we selected and the default fuse settings are exposed to the compiler. Recall that we opted to have a means of debugging the code, which resulted in the #device ICD=TRUE directive. You can also see the obvious declarations alluding to the delay functions’ time base, the LED I/O pin, and the LED alias, respectively. The final line of code in the main.h file sets up the PIC18F27J13’s EUSART with a CCS compiler #use rs232 directive. All of the directive code that follows the fuse declarations replaces code we would normally write to set up the CPU clock and LED I/O pin.

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I’ve filled in the blanks. The receive interrupt skeleton generated by the Project Wizard has been populated with a nifty serial receive interrupt handler that feeds a 256- byte circular buffer. I’ve also written a function called recvchar that pulls characters out of the circular buffer in the order in which they arrive. There’s also a routine to check for characters in the circular buffer that are yet to be retrieved. The main application blinks the activity LED every 100 mS and looks for incoming characters. All incoming characters are echoed back to the sender.