CD2481 datasheet(88/222 Pages) INTEL

88 / 222 page

CD2481 — Programmable Four-Channel Communications Controller

Datasheet

7.5.8

UNIX Support Features

COR6 provides several functions useful in UNIX TTY drivers, to further reduce the amount of

character-by-character processing 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 and character error conditions.

Break conditions can be handled in the normal way (via a receive exception interrupt), 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 (via receive exception

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 via 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. Figure 19 shows the exact order of the CD2481 character processing steps in

flowchart form.

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

≤ receive character ≤

SCRh.

Table 14. SCdet[x] Settings

SCdet2

SCdet1

SCdet0

CD2481 Datasheet(PDF) 88 Page - Intel Corporation