CD2481
—
Programmable Four-Channel Communications Controller
96
Datasheet
Key
hunt
i
CRC
0
1
STXf
SOHf
= Go to syn hunt state
= initialize BCC
= calculate CRC
= clear state flag for example, 0-RxITB clears the RxITB flag
= set state flag
= STX first flag
= SOH first flag
Note:
When returning to the syn-hunt state, RxITB is cleared.
ETB
RxITB = 0
6
hunt
4 CRC
0-RxITB
4 CRC
0-RxITB
5 CRC
CRC
b
6
7
CRC
8
PAD
6
hunt
7 CRC
3 CRC
5 CRC
CRC
b
hunt
0-RxITB
7
CRC
hunt
none of above
RxITB = 0
6
hunt
7 CRC
3 CRC
5 CRC
CRC
b
6
7
CRC
8
none of above
RxITB = 1
3 i CRC
hunt
7 CRC
3 CRC
5 CRC
CRC
b
6
7
CRC
8
1.The BDIS
’
state is entered on receipt of error.
2.In the BBCC2 state, if RxITB = 1, go to state BGETHDR, else go to syn hunt.
3.If RxITB = 1, then calculate BCC, else do not calculate BCC.
4.IF SOHf-1 and EBCDIC, then calculate BCC, else do not calculate BCC. If in ASCII/LRC mode, initialize BCC. Else do not
calculate nor initialize BCC.
5.If in ASCII/LRC mode, but overridden by the DLE-STX, then initialize BCC, else calculate BCC.
Table 15. Bisync Receive State Transition
(Sheet 2 of 2)
(see
“
Key
”
on page 96
)
Character
Received
BGETHDR
0
BESCF
1
BESCL
2
BGETxT
3
BBCC
4
BBCC2
5
BWEOT
6
BXP
7
BDIS
8
1
Equation 1. State Descriptions
Number
Name
Description
0
BGETHDR
SYN-SYN received, and looking for next non-SYN character.
1
BESCF
The first DLE after opening SYNs has been received.
2
BESCL
A DLE has been received, but not the first for this frame.
3
BGETXT
The first non-SYN character after opening SYNs has been received, and that first
character is either: STX, SOH, or a non-organized character if RxITB=1.
4
BBCC
A proper end of text has been received, and the channel is ready for the first BCC
character. The things considered proper are: ETX, ETB, or ITB in non-transparent.
Or, DLE-ETX, DLE-ETB, or DLE-ITB in transparent.
5
BBCC2
The first BCC character has been received, and the chip is ready for the second
BCC character.
6
BWEOT
Continue receiving in this state until a PAD is detected.
7
BXP
Transparent receive. Look for escape DLE. Else, keep receiving.
8
BDIS
Disconnect state. Nothing being received. Remains in this state until a PAD is
received.