CD2231 Intel Corporation, CD2231 Datasheet - Page 80

• Manufacturer Part Number: CD2231
• Description: CD2231 Intelligent Two-channel Lan And Wan Communications Controller
• Manufacturer: Intel Corporation

CD2231 — Intelligent Two-Channel LAN and WAN Communications Controller
6.5.7
6.6
80
Table 16. SCdet Settings
UNIX Support Features
The COR6 (Channel Option Register 6) provides several functions useful for UNIX TTY drivers,
to further reduce the amount of character-by-character processing that the CPU is required to
perform. Separate receive and transmit bits are provided to perform CR/NL (carriage return/new
line) translations. In transmit, NL can be converted to CR NL or CR converted to NL. In receive,
CR can be discarded, NL converted to CR, or CR converted to NL.
In receive processing, separate modes are provided to handle break conditions and character error
conditions. Break conditions can be handled in the normal way (by a receive status interrupt), or
the condition can be discarded, or the break can be translated to a NULL (00) and passed as normal
data to the CPU. Parity and framing errors can either be handled as normal (by receive status
interrupts), discarded, translated to a NULL (00) and passed to the CPU as normal data, or the
character can be passed to the CPU as normal data preceded by the sequence FF 00.
The LNext option (COR7[6]) provides a mechanism to transfer flow control and other special
characters without invoking flow control or special character interrupts at the receiver. If the LNext
option is enabled when the LNext character is received, the following character is just passed to the
CPU as a normal character. The LNext character is programmed by the LNext register. The ‘Strip’
feature (COR7[7]) strips the eighth bit off each error-free received character. It has no effect on the
transmitted data. The flowchart in
character processing steps.
Non-8-Bit Data Transfers
In Asynchronous mode, it is possible to transmit and receive less than 8 bits per character. There
can be 5, 6, 7, or 8 bits per character.
For HDLC mode, there are always 8 bits per character transmitted. The CD2231 transmits only
byte-aligned frames. The CD2231 receives HDLC frames using transfers of 8 bits per character,
except for the last character received before the FCS. If this last character is not aligned to an 8-bit
boundary, the ResInd (Residual Indication) bit is set, along with the EOF bit in RISR.
SCdet2
0
1
1
SCdet1
1
0
1
SCdet0
1
0
1
Special character 3 matched if
character 1 and 3 sequence not
enabled
Special character 4 matched if
character 2 and 4 sequence not
enabled
The hex value of the receive
character is within the range
SCRl
SCRh.
Figure 19 on page 81
receive character
Function
shows the exact order of the CD2231
Datasheet