CD1865 Datasheet, PDF (63/150 Pages) Intel Corporation – Intelligent Eight-Channel Communications Controller

Intelligent Eight-Channel Communications Controller — CD1865
The user may individually enable any CD1865 channel to recognize special characters. There are
six bits used to control the various recognition and flow-control modes.
The following four registers are used to control character recognition:
Bit Name
SCDE
RxSC
XonCH
XoffCH
Register
COR3
COR3
COR3
Function
Enables detection of special characters. Must be set for In-Band Flow
Control to work.
Enables generation of service requests. Cannot be overridden by
other bits. Does not need to be set for In-Band Flow Control to work.
Controls single- versus double-character matching.
Controls single- versus double-character matching.
The following table shows the effects of XonCH and XoffCH:
XonCH
0
0
1
1
XoffCH
0
1
0
1
Characters matched
Match on: any of SCHR1–4
Match on: SCHR1 or SCHR3 or (SCHR2 and SCHR4)
Match on: (SCHR1 and SCHR3) or SCHR2 or SCHR4
Match on: (SCHR1 and SCHR3) or (SCHR2 and SCHR4)
Note: The two-character pairs can share a common first character; however, the same character must be
programmed in both SCHR1 and SCHR2.
Single- versus double-character recognition is controlled by XonCH and XoffCH. If single-
character compare is enabled, the CD1865 compares data in the data stream against the four special
characters stored in the Special Character registers (SCHR1-4). If fewer than four special
characters are required, the unused Special Character register(s) should be disabled by duplicating
the pattern to be matched in the unneeded register. When reporting a special character, the CD1865
always reports the lowest-number Special Character register that matches.
To set up Special Character Recognition, first set the characters to be matched in registers SCHR1-
4, then set XonCH and XoffCH according to the length of match wanted. Set the SCDE bit, and
lastly enable service requests by setting RxSC.
Special characters are reported to the host by placing the appropriate status word in the Status FIFO
and the recognized special character in the Receive Data FIFO. In the case of a two-character
sequence, only the second character is stored in the Receive FIFO. This is because there is room
only for one character and preserving both is not needed as these characters are user-defined.
7.1.9
Flow-Control Characters
Automatic In-Band Flow Control of the CD1865 transmitter is a subset of the Special Character
Recognition capability, so to understand both these features is important. Refer to Section 7.2 on
page 68 for transmitter operation. Flow-control characters and operation are programmable on a
per-channel basis. This is important to operating systems that allow users to configure their own
terminal settings independently.
Datasheet
63