AN2502 Freescale Semiconductor / Motorola, AN2502 Datasheet - Page 2

• Manufacturer Part Number: AN2502
• Description: Using Two Channels of the HC08 TIM to Achieve a Full-Duplex Software SCI
• Manufacturer: Freescale Semiconductor / Motorola

AN2502/D
Modes
Normal Mode
2
Using Two Channels of the HC08 TIM to Achieve a Full-Duplex Software SCI
The time required for sending a byte is 10 bit-times. A bit-time is equal to
1/baud rate. For example, if the baud rate is 9600 bps, the entire frame takes
1.0416 ms.
The transmission begins with a high-to-low transition as soon as the bus is in
idle state; that is, in logic high for more than 10 bit-times. Next, the desired byte
is transmitted with its least significant bit first. A byte transmission is ended with
a logic level high known as the stop bit, which indicates that a transmission is
finished. See
The channel used for reception is configured as an input capture on the falling
edge to detect a high-to-low transition known as the start bit. When this event
occurs, the input capture operation will “capture” the time at which the event
occurred. Because this pin logic is hardware implemented in the HC08 MCU,
the exact time of the beginning of the reception is captured.
Two operation modes of the software-implemented SCI are presented in this
document: normal mode and enhanced mode.
Features of normal mode:
START
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Freescale Semiconductor, Inc.
BIT
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Full-duplex operation
Minimal code size
Minimal software overhead
Easily configured for different baud rates
Interrupt request by each reception bit
Uses less CPU time and memory space than enhanced mode
No error detection available
No receiver full or transmitter empty subroutine available
One fixed data format: eight data bits and one stop bit
BIT 0
Figure 1. Non-Return-to-Zero Mark/Space Data Format
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Figure
BIT 1
BIT 2
1.
BIT 3
BIT 4
BIT 5
BIT 6
BIT 7
PARITY
BIT 8
BIT
STOP
BIT
MOTOROLA
START
NEXT
BIT