AN2502 Freescale Semiconductor / Motorola, AN2502 Datasheet - Page 9

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

MOTOROLA
Using Two Channels of the HC08 TIM to Achieve a Full-Duplex Software SCI
must be added to the reception channel to check the pin at the correct time.
Figure 15
For proper operation, the instruction that checks the pin state must be executed
after 0.3 of the bit-time and before 0.7 of the bit-time. This is accomplished by
adding 1.3 bit-times to the reception channel as soon as the start bit has been
detected. In the output compare interrupt for the reception channel, several
instructions are executed before the pin check instruction. These instructions
are collectively called the pin check latency in this application note.
Figure 16
Figure 17
to the last data bit receptions is 1 bit-time.
Freescale Semiconductor, Inc.
For More Information On This Product,
The time added
after the start bit for
the first data bit
reception
shows that the time added to the reception channel between the first
shows the first data bit reception.
illustrates how to calculate the correct time added after the start bit.
Go to: www.freescale.com
0.3 BIT-TIME
Figure 16. Time Added After the Start Bit
0.3 BIT-TIME
Figure 15. First Data Bit Reception
START BIT
Figure 17. Data Bit Reception
=
Start bit reception
time stored in the
reception channel
registers
1 BIT-TIME
DATA BIT
FIRST
FIRST OUTPUT COMPARE
1 BIT-TIME
DATA BIT
FIRST
SECOND
DATA BIT
+
30% of 1
bit-time
0.7 BIT-TIME
–
pin check
latency
AN2502/D
Modes
9