Mitsubishi Digital Electronics FX0N Manual

A SERVICE OF

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FX Series Programmable Controllers Points Of Technique 10

10-19

10.14.2 Header and Terminator Characters

The header and terminator characters can be chan

g

ed b

y

the user to suit their requirements.

The default settin

g

for the header stored in D8124 is 'STX' (or 02H)and the terminator default

settin

g

stored in D8125 is 'ETX' (or 03H).

The header and terminator characters are automaticall

y

added to the 'send' messa

g

e at the

time of transmission. Durin

g

a receive c

y

cle, data will be i

g

nored until the header is received.

Data will be continuall

y

read until either the termination character is received or the receive

buffer is filled. If the buffer is filled before the termination character is received then the

messa

g

e is considered incomplete.

If no termination character is used, then readin

g

will continue until the receive data buffer is

full. Onl

y

at this point will a messa

g

e have been accepted and complete. There is no further

bufferin

g

of an

y

communications, hence if more data is sent than the available destination

buffer size then the excess will be lost once the buffer is full.

It is therefore ver

y

important to specif

y

the receive buffer len

g

th the same size as the lon

g

est

messa

g

e to be received.

Events to complete a transmission:

The RS instruction should be set up and active.

The data to be transmitted should be moved into the

transmission data buffer. If a variable is bein

g

used to

identif

y

the messa

g

e len

g

th in the RS instruction this

should be set to the new messa

g

e len

g

th. The send fla

g

M8122 should then be SET ON. This will automaticall

y

reset once the messa

g

e has been sent. Please see the

example pro

g

ram ri

g

ht.

Events encountered when receiving a message:

The RS instruction should be set up and active.

Once data is bein

g

received and an attempt is made to

send out data, the special M fla

g

M8121 is set ON to

indicate the transmission will be dela

y

ed. Once the

'incomin

g

' messa

g

e is completel

y

received the messa

g

e

received fla

g

M8123 is set ON. At the same time if M8121

was ON it is automaticall

y

reset allowin

g

further

messa

g

es (dela

y

ed or otherwise) to be transmitted.

It is advisable to move the received data out of the received data buffer as soon as possible.

Once this is complete M8123 should be reset b

y

the user. This is then read

y

to send a

messa

g

e or to await receipt of a new messa

g

e.

K 10D200RS D49D50

M8000

X3

BMOV K 6D50D100

MOV D49K6

SET M8122

K 10D200RS D49D50

M8000

M8123

BMOV K 10D70D200

RST M8123