e001046.pdf

MICROPROCESSORS

network (CAN) (5)

Part 5:

a CAN interface using BASIC537

If you are new to the

CAN bus, look for-

ward to some hard

work before seeing

the first usable

results. After all, at

least two microcon-

troller systems have

to be hooked up to

CAN bus controllers,

and a bus-based data link implemented based on the use of talk/listen

programs. Once you have data travelling over the bus, all further expan-

sion is really simple. This article attempts to make your first practical

experiments with the CAN bus as easy as possible.

Hardware & software design

by B. Kainka

The CAN bus interface described in

Elektor Electronics November 1999 may

be controlled using the BASIC537

higher programming language.

BASIC537 is an EPROM version of the

well-known Intel MCS51 BASIC, spe-

cially adapted and extended for the

80C537 microcontroller. Many of you

will be familiar with MCS51 BASIC

because it was the subject of several

articles in Elektor Electronics . Originally,

this BASIC interpreter was developed

for the (now obsolete) 8052AH-BASIC

microcontroller. When stored in an

external (E)PROM, however, it is also

great for other controllers from Intel’s

80xx series and second sources (see

also the 80C32 BASIC Control Com-

puter described in Elektor Electronics

February and March 1998). The 537

‘Lite’ Computer is described elsewhere

in this magazine — it too is capable of

running BASIC537. The ancestor of this

computer, a full-blown 80C357 micro-

controller system, was published in our

June 1997 magazine.

The new, smaller and cheaper 537

‘Lite’ Computer is employed here in

Elektor Electronics

1/2000

controller area

combination with the CAN bus inter-

face. The 537 ‘Lite’ is prominently fea-

tured on this month’s cover.

PFI

PFO

RESET

ALE

INT4

INT3

INT6

INT5

INT2

T2EX

CLKO

INT1

INT0

VAREFF

H ARDWARE

An adaptor board was developed to

implement a simple connection

between the 537 ‘Lite’ Computer (fitted

with a BASIC537 EPROM) and the

CAN interface board. The circuit dia-

gram of the adaptor is given in Fig-

ure 1 , the copper track layout and com-

ponent mounting plan, in Figure 2 . As

you can see on the photograph, there

are no wiring problems because the

537 ‘Lite’ board is plugged directly on

to the adaptor board. The link with the

CAN interface is then made using a

length of flatcable (see introductory

photograph).

To solve the power supply problem

in a simple way, a 5-volt voltage regu-

lator and supply reversal protection are

accommodated on the adaptor board.

In this way, the adaptor board can sup-

ply +5 V to the two other boards. The

upshot is that any low-cost wall adaptor

supplying 9-12 volts unregulated at

about 300 mA may be connected to

PCB connector K2. If you already have

a stabilized 5-volt line available, you

may omit IC1, D1, C1 and C2 from the

adaptor board, and

connect the 5-V supply

voltage directly to the

K1 terminals on the

adaptor board.

To keep cost down,

the adaptor board is

much smaller than the

537 ‘Lite’ Computer board to be

plugged on it. If you cut the adaptor

board in two along the line indicated

on the PCB overlay, and fit the two

sub-boards at the right distance above a

carrier (e.g. aluminium sheet), the 537

‘Lite’ Computer is easily plugged on to

this assembly. The only wire connec-

tion to make (if necessary) is INT2

between pin 12 (K3) and pin 32 (K6)

(see the photograph showing the 537

‘Lite’ Computer board with the two

adaptor sub-boards). The two adaptor

sub-boards have connecting pins for

the INT2 link, which is also shown as a

wire link on the component mounting

overlay (Figure 2).

VOUT

VBATT

CS2

ALE

INT2

RESET

A15

A14

A13

A12

A11

A10

P47

P46

P45

P44

P43

P42

+5V

P41

P40

P67

P66

P65

IC1

P63

1N4001

P64

7805

P60

P50

P51

P52

P53

P54

P55

P56

P57

PSEN

CS0

CS1

CS2

+9V

10µ

16V

100n

10µ

16V

100n

990066 - 4 - 14

Figure 1. Circuit diagram of an

adaptor board that creates a

simple link between the 537

‘Lite’ Computer board and the

CAN bus interface.

The essential

settings are

supplied as

defaults by the

program. The

communication runs at 20 kbits/s. Mes-

sage are sent without the RTR bit — in

other words, no reply is requested. The

two systems should fulfil the following

functions:

noted between the termination resis-

tors being present or not.

T RANSMIT PROGRAM

AND TEST

The transmit program for Controller 1 is

given in Listing 1 . The CAN controller

SJA1000 is addressed by the 80537 sys-

tem via base address 0F000h. The

address range is defined in line 95

(BA=0F000h). If you use a different

system, all you have to do (initially) is

modify BA accordingly. The initialisa-

tion is carried out as described in the

article on the CAN bus interface hard-

ware. In lines 110 and 200, the results

of the register programming are

requested. The program then waits for

a register bit to go to a specific state. In

case the controller is not found on the

bus, or does not function correctly, the

program will ‘hang’ at this point. If

everything is successful, however, you

are greeted with these messages:

System 1 regularly sends messages

with Identifier 300 and containing

eight bytes. The data originates from

the first eight channels of the A-D con-

verter. The system continuously per-

forms measurements on eight ana-

logue inputs. The messages it transmits

may be received and processed by any

other system connected to the bus.

System 2 receives all messages on the

bus and copies them to the PC by way

of the RS232 interface. In fact, this is a

simple CAN monitor that allows you to

pick up and examine all data traffic on

the CAN bus.

C ONTROL IT ALL IN

BASIC

In essence, all you need to be able to

control the CAN interface board is a

program that looks after a bank of reg-

isters starting at address F000h in the

CAN controller SJA1000. The XBY

operator is employed for all access to

addresses in the external RAM area

and peripherals.

To make the introduction as easy

going as possible, the following para-

graphs describe the simplest case of a

data link between two 80C537 systems.

Reset OK

Init OK

A block diagram of the system config-

uration is given in Figure 3 . A special

cable is not required to link the two

systems. Our first experiments in the

lab indicated that a simple two-wire

link between pins 4 and 8 of the CAN

plugs is adequate if the total length

does not exceed about 1 metre. With

such a short cable, no difference was

To start with, it is sufficient to execute

the initialisation routine up to line 200.

An initial check may be made by look-

ing for a rectangular signal at the test

pin on the controller board. Whereas

this pin supplies 8 MHz before the ini-

tialisation, you will then find 2 MHz. If

this is okay so far, you may safely

Elektor Electronics

1/2000

COMPONENTS LIST

Capacitors:

C1, C3 = 10 µ F 16V (radial)

C2, C4 = 100nF (ceramic)

Semiconductors:

D1 = 1N4001

IC1 = 7805

Miscellaneous:

K1 = 2-way PCB terminal block,

raster 5mm

K2 = 2-way PCB terminal block,

raster 5mm

K3 = boxheader, straight, 16 pins

K4 = pin header, 1 row, 4 pins

K5, K6 = pin header, one row,

straight, 35 pins

IC1

Figure 2. Layout and com-

ponent mounting plan of

the adaptor board.

assume that the controller is driven

with the proper signals.

Now the complete program may be

loaded and executed. Experienced as

you are, you will no doubt have an

oscilloscope ready to observe data traf-

fic on the bus. Without a connection

having been made to a second system,

you will be able to find signals on the

data lines. After a hardware reset and

without an initialisation you will not be

able to find the ‘inactive’ level of 2.5 V

s long, which means that

the transmission rate is indeed

20 kBits/s. However, you will not fail to

see that there is a quasi-steady datas-

tream with 2-ms pauses, rather than

short data packets as would be

expected. Not to worry, however, this

is the normal behaviour of the con-

Figure 3. Block diagram

showing how the CAN bus

is linked to the two 80537

systems programmed in

537 BASIC.

troller as long as it has not detected any

intelligence on the CAN bus. Yet, it is

not sufficient to connect the second

controller via the two-wire link,

because this, like system 1, has to be

initialised. By the way, the transmitting

station will continue to send a quasi-

continuous datastream even if the

BASIC program is terminated.

A T THE

RECEIVER SIDE

Now we are ready to ‘deploy’ the

receiver program as given in Listing 2 .

This program is for system number 2.

As you can see from the listing, the ini-

tialisation is the same as that used for

the transmitter. As soon as the initiali-

sation is done and the message “Init

OK” has appeared on the PC display,

the transmitting controller will com-

Elektor Electronics

1/2000

on the two wires. As soon as the trans-

mit program is started, data is easily

recognized as rectangular signals with

a level of 1 V. The shortest logic levels

are just 50

mence its normal operation. From then

on, short data packets with a length of

just over 5 ms will start to appear on

the CAN bus. Finally, the CAN bus

functions as you, the interested reader,

would like to see it: data packets being

sent back and forth over the bus with-

out any indication of their being read

anywhere at all!

The actual receiver program starts

at line 500 and waits for a message

which is announced by controller sta-

tus bit zero. As soon as a data packet

has arrived, the program may read ten

bytes from the controller. The first two

contain the message ID. It is recovered

from two bytes in line 570 and then

sent to the display. As expected, it is the

‘ID’, 300, which was arbitrarily defined

in the transmitter program.

Listing 1. Transmitter program CAN1.BAS.

90 REM Init CAN Controller

95 BA=0F000H

100 XBY(BA+00H)=01H : REM Reset Mode

110 IF (XBY(BA+00H).AND.1)<>1 THEN GOTO 110

111 PRINT ”Reset OK”

120 XBY(BA+1FH)=43H : REM CDR, 2 MHz

130 XBY(BA+04H)=0 : REM ACR

140 XBY(BA+05H)=0FFH : REM AMR, Acceptance Mask, all

150 XBY(BA+06H)=53H : REM BTR0, 20 Kbit/s*

160 XBY(BA+07H)=2FH : REM BTR1

170 XBY(BA+08H)=1AH : REM OCR;

180 XBY(BA+01H)=0EH : REM CMR, end sleep mode

190 XBY(BA+00H)=0 : REM CR, end reset mode

200 IF (XBY(BA+00H).AND.1)>0 THEN GOTO 200

201 PRINT ”init ok”

500 REM ************* Main Loop ***************

501 REM Send 8 Bytes of AD-Data in message 300

510 FOR N=0 TO 7

520 XBY(BA+0CH+N)=AD(N) : REM fill TB1..TB8

530 NEXT N

540 ID=300 : REM Message Identifier

550 DFL=8 : REM 8 Bytes

560 GOSUB 1000 : REM Send Massage

570 FOR T=1 TO 1000 : NEXT T

580 GOTO 500

1000 REM ************* Send CAN Telegram *************

1010 IF (XBY(BA+02H).AND.4)=0 THEN GOTO 1010 : REM SR

1020 XBY(BA+0AH)=INT(ID/8) : REM IDT1

1030 XBY(BA+0BH)=(ID-8*INT(ID/8))*32+DFL : REM IDT2

1040 XBY(BA+01H)=0DH : REM CMR, start transmission

1050 RETURN

Listing 2. Receiver program CAN2.BAS

The user data are read in a loop and

displayed in line 610. There , you

(finally…) get the measured values on

the eight analogue inputs of the first

controller system. Figure 4 shows the

received data in a terminal window.

90 REM Init CAN Controller

95 BA=0F000H

100 XBY(BA+00 H)=01H : REM Reset Mode

110 IF (XBY(BA+00H).AND.1)<>1 THEN GOTO 110

111 PRINT ”Reset OK”

120 XBY(BA+1FH)=43H : REM CDR, 2 MHz

130 XBY(BA+04H)=0 : REM ACR

140 XBY(BA+05H)=0FFH : REM AMR, Acceptance Mask, all

150 XBY(BA+06H)=53H : REM BTR0, 20 Kbit/s*

160 XBY(BA+07H)=2FH : REM BTR1

170 XBY(BA+08H)=1AH : REM OCR;

180 XBY(BA+01H)=0EH : REM CMR, end sleep mode

190 XBY(BA+00H)=0 : REM CR, end reset mode

200 IF (XBY(BA+00H).AND.1)>0 THEN GOTO 200

201 PRINT ”Init OK”

500 REM ******* Receiver Main Loop *************

510 SR=XBY(BA+02H) : REM Status Register

520 REM Error Detection and Clear Data Overrun

530 if (SR .AND. 2) = 2 then XBY(BA+01H)=8: :Goto 510

540 REM Get Receive Status

550 if (SR .AND. 1) =0 then goto 510

560 REM Read received message

570 ID=XBY(BA+14H)*8+INT(XBY(BA+15H)/32) : PRINT ID

580 DFL=XBY(BA+15H).AND.15 : rem Data Length

590 RTR=(XBY(0FE15H).AND.16)/16 : REM RTR not used

600 FOR N=0 To 7

610 PRINT N ,XBY(BA+16H+N)

620 NEXT N

630 XBY(BA+01H)=0CH : REM Release Receive Buffer

640 GOTO 510

F INALLY :

THREE ON THE BUS

Of course, the results up to now could

have been obtained with a rather sim-

pler RS232 interface. The CAN bus

however will typically not unleash its

power until more than two devices are

connected to the bus. To end the

‘lonely’ existence of the two systems

discussed so far, a third ‘CANable’

device should be added. The program

CAN3.BAS shown in Listing 3 (with-

out initialisation!) performs the follow-

ing functions:

Elektor Electronics

1/2000

Listing 3. Receiver & Transmitter program CAN3.BAS

without initialisation.

650 WRSFR 0E8H,PORT : REM Port 4 Output

660 XBY(BA+01H)=0CH : REM Release Receive Buffer

800 REM ******** Send AD-Data ***********

810 FOR N=0 TO 7

820 XBY(BA+0CH+N)=AD(N) : REM fill TB1..TB8

830 NEXT N

840 ID=500 : REM Message Identifier

850 DFL=8 : REM 8 Bytes

860 GOSUB 1000 : REM Send Message

870 FOR T=1 TO 1000 : NEXT T

880 GOTO 500

1000 REM ******* Send CAN Telegram *************

1010 IF (XBY(BA+02H).AND.4)=0 THEN GOTO 1010 : REM SR

1020 XBY(BA+0AH)=INT(ID/8) : REM IDT1

1030 XBY(BA+0BH)=(ID-8*INT(ID/8))*32+DFL : REM IDT2

1040 XBY(BA+01H)=0DH : REM CMR, Start Transmission

1050 RETURN

500 REM ************ Main Loop ***************

505 REM ************ Receiver ****************

510 SR=XBY(BA+02H) : REM Status Register

520 REM Error Detection and Clear Data Overrun

530 IF (SR.AND.2)=2 THEN XBY(BA+01H)=8 : GOTO 510

550 IF (SR.AND.1)=0 THEN GOTO 510

560 REM Read received message

570 ID=XBY(BA+14H)*8+INT(XBY(BA+15H)/32): Print ID

580 DFL=XBY(BA+15H).AND.15 : REM Data Length

590 RTR=(XBY(0FE15H).AND.16)/16 : REM RTR not used

600 IF ID<>300 THEN GOTO 660

610 PORT=0

620 IF XBY(BA+16H+0)>100 THEN PORT=PORT+1

630 IF XBY(BA+16H+1)>100 THEN PORT=PORT+2

640 IF XBY(BA+16H+2)>100 THEN PORT=PORT+4

Figure 4. Received

data in the terminal

window of BASIC537.

It receives all messages but only

processes the ones with the ID ‘300’.

The first three transmitted measure-

ment values are compared with certain

extreme values and switch on three

lines on Port 4 if a particular extreme is

exceeded.

After processing of the received

message, a message with the ID ‘500’ is

returned, where all A-D channels are

measured and transmitted again. As

soon as the third system is connected

to the bus, System 2 will also supply

data with ID ‘500’ to the terminal (see

Figure 5 ).

990066-4

Note: the three program listings dis-

cussed in this article are available for

downloading from the Elektor Elec-

tronics website at www.elektor-electron-

ics.co.uk

Article editing (German original): E. Krempelsauer

Design editing: K. Walraven

Figure 5. Reception of

messages with Identi-

fiers (IDs) ‘300’ and

‘500’.

Elektor Electronics

1/2000

Plik z chomika:

Inne pliki z tego folderu:

Inne foldery tego chomika: