Industrial Communication Systems

Modbus 36-11

sequence “CR” “LF” occurs. Since this mode does not specify a maximum time interval between con-

secutive

characters,

this

implies

that

this

interval

could

theoretically

assume

any

value.

However,

this

could

lead

to

a

situation

in

which

the

receiver

would

block,

e.g.,

when

the

sender

crashes

during

a

frame

transmission,

whereupon

the

receiver

would

wait

indenitely

for

the

remaining

characters.

In

order

to

prevent

these

situations,

the

receiver

should

implement

a

timeout

mechanism.

When

a

timeout

occurs,

the

received

data

are

discarded

and

the

receiver

waits

for

the

next

frame.

In

[4],

it

is

suggested

to

use

1

s

for

the

timeout

value.

However,

it

is

possible

to

use

other

values

depending

on

the

network

topology.

Further

de

tai