AN1212 Freescale Semiconductor / Motorola, AN1212 Datasheet - Page 16

• Manufacturer Part Number: AN1212
• Description: J1850 Multiplex Bus Communication Using the MC68HC705C8 and the SC371016 J1850 Communications Interface (JCI)
• Manufacturer: Freescale Semiconductor / Motorola

AN1212/D
16
39
OSC1
OSC1
M
C
6
8
H
C
7
0
5
C
8
4 MHz
1 M
OSC2
OSC2
MISO
MOSI
SCK
PC1
PC0
IRQ
V
V
SS 34
DD
SS
38
2 x 27 pF
33
31
32
28
27
32
40
20
+5 V
10 k
0.1 F
+5 V
J1850 Multiplex Bus Communication Using the MC68HC705C8
15
11
12
13
14
and the SC371016 J1850 Communications Interface (JCI)
3
4
5
7
9
Figure 8. Example MUX Bus Interface Circuit
This software is intended to be a basic implementation, consuming less than
400 bytes of ROM, so of course the user’s system requirements may call for
different, and possibly more enhanced, routines. However, these routines
should give any potential user a good basic introduction to interfacing the JCI
to an MCU, and they can easily be enhanced where added features are
needed. Though the MC68HC705C8 is the MCU which was utilized in this
example, these driver routines can easily be used with any member of the
M68HC05 or M68HC11 Families which has an SPI, a 16-bit timer, and an
appropriate amount of memory for the user’s application.
This software is written for enhanced SPI mode which requires a little more
CPU overhead but fewer host MCU I/O lines. An I/O line of the host MCU is also
connected to the RESET input of the JCI, giving the host MCU the ability to
reset the JCI through software whenever appropriate. The circuit in
shows a basic JCI/host MCU interface with the JCI configured for 10.4 kbps
VPW transmission and IFR required for each message. The physical address
of the node depicted is $55. These hardware assumptions are reflected in the
software routines, as is the use of three-byte headers, but these routines will
work quite well with any hardware configuration required by the user.
SCK
SDO
SDI
RESET
CS
INT
MODE0
MODE1
COMSEL
V
SS
Freescale Semiconductor, Inc.
OSC1
For More Information On This Product,
1
4 MHz
1 M
S
C
3
7
1
0
1
6
OSC2
Go to: www.freescale.com
2
2 x 27 pF
V
RxJ
IFR
TxJ
ID6
ID4
ID2
ID0
ID7
ID5
ID3
ID1
DD
28
17
26
24
22
20
19
18
27
25
23
21
10 k
10 k
10 k
10 k
10 k
0.1 F
+5 V
+5 V
1
2
3
5
4
*The JVT is a proposed J1850 VPW transceiver
INV
TxD
V
DE
RxD
DD
J*
V
T
V
BATT
V
Rx
Rs
Tx
SS
+ 12 V
8
11
9
7
6
1 k
20
22 k
1.5 k
3300 pF
MOTOROLA
Figure 8
3.3 V
33 V
J1850
BUS