Dual RS232 Communication Routine
with LCD display and two MAX232 for
PIC16F77
Table of Contents [Toc]
Concept
Specifications
Project Resources
Available Microchip PIC
Assembler Source Code
Concept [Toc] [Top]
Two independent RS232 interfaces, with display of received
ASCII characters and corresponding decimal values on the dot matrix
LCD. ASCII values entered on one terminal window are transmitted
by the first RS232 link to the controller, displayed on the LCD,
and further transmitted across the second RS232 link to the other
terminal window. The microcontroller sends feedback of received
characters back to the issueing terminal window. When the PIC
terminal is idle, it sends a status message '@' to both terminals
every 2.75 seconds.
This program incorporates two independent RS232 interfaces,
one hardware-based and one software-based. The HW-based RS232
interface uses the PIC-internal USART (and interrupts), configured
to standard 9600 baud @ 4 MHz PIC clock. The SW-based RS232 interface
is based on the module file m_rs096.asm, which performs interrupt-based
RS232 reception on PortB0 (INTCON,INTF) at 9600 baud @ 4 MHz PIC
clock.
The program shows the implementation and function of the modules
m_bank.asm, m_wait.asm, m_lcd.asm, m_lcdv08.asm, and m_rs096.asm
on the PIC16F77.
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Dot matrix LCD display
showing output after having received 'a' from the first
RS232 terminal and 'b' from the second RS232 terminal. Every
character received is displayed in both ASCII and decimal value,
and then transmitted to the other RS232 terminal across the second
communication link. |
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PIC16F77 test board with two MAX232
Test setup using onboard MAX232 and additional external MAX232
to serve both RS232 links. The PIC controller now serves two
asynchronous RS232 connections, one in software mode using interrupts
and one using the hardware USART of the PIC16F77. |
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Screen shot of the two HyperTerminal Programs
using the dual RS232 communication routine. The left window configured
to ComPort 5 represents the first link, the right window configured
to ComPort 7 represents the second link. After power-up and welcome
message, the message 'Hello World' was entered at the left terminal
window, then the message 'I say also hello' was transmitted using
the right terminal window. |
Specifications [Toc] [Top]
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Processor: |
Microchip PIC 16F77 |
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Clock Frequency: |
4 MHz crystal |
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Throughput: |
1 MIPS |
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RS232 Configuration: |
9600 with BRGH = 1 |
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RS232 Baud Rate: |
9600 baud, 8 bit, no parity, 1 stopbit |
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Code Size of entire Program: |
approx. 733 instruction words |
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Acquisition Methodology: |
SW-based RS232: Interrupt-based RS232 data acquisition
HW-based RS232: Preemptive, interrupt-based RS232 data acquisition,
LCD display output and RS232 echo during normal operation |
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Required Hardware: |
two MAX 232 for two RS232 interfaces, dot matrix LCD display |
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Required Software: |
RS232 terminal software (or Excel 97 RS232 Debug Interface) |
Project Resources [Toc] [Top]
Available Microchip PIC Assembler
Source Code [Toc]
[Top]
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Main File |
HEX Files |
Download assembler source code:
16F77dual.asm |
Download Hex File:
16F77dual.hex |
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The above program needs additional include files (modules) to get successfully assembled: m_bank.asm,
m_wait.asm, m_lcd.asm |
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For those, who are not familiar with interfacing a PIC to the
RS232 using a MAX232: RS232-Interface.pdf
(9.7 kB) |
Download ASCII Character Map: ASCII-Map.pdf
Last updated: 16.01.2005
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