AN2502 Freescale Semiconductor / Motorola, AN2502 Datasheet - Page 20

• 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
Full-Duplex Maximum
Baud Rate
Hardware
20
15pF
C6
9.8304 MHz
Y1
Using Two Channels of the HC08 TIM to Achieve a Full-Duplex Software SCI
VCC
C7
15pF
Figure 28. HC08 to MAX232 Interface Connection
When receiving data in the full-duplex operation based on
the input pin for the bit being received must be performed within 30% and 70%
of 1 bit-time to check the state of the pin in the center. For full-duplex operation,
the value of the bit-time multiplied by 0.4 (70% to 30%) in timer counts must be
greater that the number of cycles for the transmission interrupt. Therefore, if the
transmission interrupt arrives before the reception interrupt, as may happen as
a worst case, the reception line will be checked in the 70% of the bit-time.
When transmitting data in the full-duplex operation, both reception and
transmission interrupts must be completed in fewer cycles than the bit-time in
timer counts. Both boundaries are taken into account to calculate the maximum
baud rate (BR) in which the SCI will fit. The following formula shows this
boundary:
Max. BR = f
Figure 28
physical interface.
10
1
2
3
4
5
6
7
8
9
Freescale Semiconductor, Inc.
IRQ1
VSS
OSC1
OSC2
VDD
PTB7/ADC7
PTB6/ADC6
PTB5/ADC5
PTD7
PTD6
U2
For More Information On This Product,
MC68HC908JK3
shows the connection between the HC08 MCU and a MAX232
Bus
PTD2/ADC9
PTD3/ADC8
PTD4/TCH0
PTD5/TCH1
PTB0/ADC0
PTB1/ADC1
PTB2/ADC2
PTB3/ADC3
PTB4/ADC4
Go to: www.freescale.com
/(MAX(max. cycles Tx/0.4, max. cycles Rx + max. cycles Tx)
RST
20
19
18
17
16
15
14
13
12
11
C1
1uF
C2
1uF
C4
1uF
C5
1uF
+
+
C8
0.1uF
+
+
VCC
+
13
11
10
8
1
3
4
5
2
6
C3
1uF
U1
MAX232
R1IN
R2IN
T1IN
T2IN
C1+
C1-
C2+
C2-
V+
V-
R1OUT
R2OUT
T1OUT
T2OUT
12
9
14
7
Figure
15, a read of
5
9
4
8
3
7
2
6
1
MOTOROLA
P1
DB9