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PDF AN1240 Data sheet ( Hoja de datos )
| Número de pieza | AN1240 | |
| Descripción | HC05 MCU Software-Driven Asynchronous Serial Communication Techniques Using the MC68HC705J1A | |
| Fabricantes | Motorola Semiconductors | |
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Freescale Semiconductor, Inc.
by AN1240/D
MOTOROLA
SEMICONDUCTOR
APPLICATION NOTE
AN1240
HC05 MCU Software-Driven Asynchronous
Serial Communication Techniques
Using the MC68HC705J1A
By Scott George
CSIC MCU Product Engineering
INTRODUCTION
This application note describes a method for asynchronous serial communication with a microcontroller
unit (MCU) using standard input/output (I/O) port pins and software which incorporate noise and frame-
error detection. If error detection is not needed, the code size may be reduced for more efficient use of
memory.
OVERVIEW
A serial communication interface (SCI) is a serial I/O sub system available with many Motorola MCUs. This
hardware module provides full-duplex, universal asynchronous receiver/transmitter-type (UART) serial
communication between the MCU and other UART-type devices, such as a cathode-ray-tube (CRT)
terminal, personal computer, or other MCUs. The SCI handles all transmission and reception duties and by
so doing off-loads the CPU to perform other functions simultaneously. The SCI is software programmable
for many different baud rates. The receiver can detect error conditions automatically, such as framing,
noise, and overrun.
Some Motorola MCUs do not include an SCI, specifically a low-cost, low-pin-count MCU such as the
MC68HC705J1A. To perform asynchronous serial communication, software must be used to emulate an
SCI. In this case, the CPU would control I/O port pins to perform the same functions as the receive data
(RXD) and transmit data (TXD) pins of a true hardware-driven SCI.
This application’s software solution requirements are:
• Speed optimization for maximum baud rate
• Minimal code size
• Easy configuration for different baud rates
• Ability to detect noise and framing errors while receiving.
Because the CPU is not as efficient as a dedicated hardware SCI, software emulation has limitations:
• Very fast baud rates are not attainable
• SCI software consumes memory space and CPU bandwidth
• Flexibility and features are reduced
©MOTOROLA INC., 1995
For More Information On This Product,
Go to: www.freescale.com
AN1240/D
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CONCLUSION
SCI receiver and transmitter software routines offer the application designer an alternative to using a
hardware SCI. The software routine listings contain the operational details. The routines may be used as
listed or customized as determined by engineering requirements.
An electronic listing of the source code in Appendix C can be found on the Motorola MCU BBS. The BBS
phone number is (512) 891-3733. The file name is J1A_5407.ARC and can be found on the CSIC BBS
under the APPNOTES directory.
AN1240/D
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Go to: www.freescale.com
MOTOROLA
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GET_CHAR
COUNT = 8
NOISE REG = 0
RXD IDLE?
YES
NO
START BIT
BEGUN?
NO
YES
PREPARE FOR 1/2
BIT DELAY
CALL DELAY_13A
CALL GET_BIT
FALSE
START?
NO
YES
PREPARE FOR 1
BIT DELAY
CALL DELAY_13A
CALL GET_BIT
SHIFT NOISE BIT
INTO NOISE REG
SHIFT DATA BIT
INTO CHAR
PREPARE FOR 1
BIT DELAY
CALL DELAY_13A
DECREMENT
COUNT
NO
COUNT = 0?
YES
CALL GET_BIT
NOISE?
YES
NO
XOR NOISE DATA
WITH CHAR DATA
NOISE?
NO
YES
SET HALF-CARRY
BIT
COMPUTE FRAME
ERROR BIT
PUT FRAME BIT
INTO CARRY
RETURN
AN1240/D
For More Information On This Product,
Go to: www.freescale.com
MOTOROLA
11
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11 Page | ||
| Páginas | Total 22 Páginas | |
| PDF Descargar | [ Datasheet AN1240.PDF ] | |
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