Chapter 6. Serial I/O, SNP & RTU Protocols
GFK-2222AD
April 2018
211
6.2.5
Overlapping COMMREQs
Some Serial I/O COMMREQs must complete execution before another COMMREQ can be processed.
Others can be left pending while others are executed.
COMMREQS that Must Complete Execution
■
Autodial (4400)
■
Initialize Port (4300)
■
Set Up Input Buffer (4301)
■
Flush Input buffer (4302)
■
Read port status (4303)
■
Write port control (4304)
■
Cancel Operation (4399)
■
Serial Port Setup (FFF0)
COMMREQs that can be Pending While Others Execute
The table below shows whether Write Bytes, Read Bytes and Read String COMMREQs can be pending
when other COMMREQs are executed.
NEW COMMREQ
Currently-Pending
COMMREQs
A
u
tod
ial
(4400
)
Wr
ite
B
y
tes
(4401
)
Initiali
ze
P
ort
(4300
)
S
et
U
p
Inp
u
t
B
u
ffer
(
4
3
0
1
)
Flu
sh
Inp
u
t
B
u
ffer
(4302
)
Read
Po
rt
S
tat
u
s
(4
3
0
3
)
Wr
ite
Po
rt
Co
nt
rol
(4304
)
Read
B
y
tes
(4402
)
Read
S
tr
ing
(4403
)
Cancel
Op
er
at
io
n
(4399
)
S
er
ial
P
ort
S
et
u
p
(
FFF
0
)
Write Bytes
(4401)
No
No
Yes
Yes
Yes
Yes
Yes
Yes
Yes
Yes
No
Read Bytes
(4402)
No
Yes
Yes
No
No
Yes
Yes
No
No
Yes
No
Read String
(4403)
No
Yes
Yes
No
No
Yes
Yes
No
No
Yes
No
