
CD2481
—
Programmable Four-Channel Communications Controller
88
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.
0
1
1
Special character 3 matched if
character 1 and 3 sequence not
enabled
1
0
0
Special character 4 matched if
character 2 and 4 sequence not
enabled
1
1
1
The hex value of the receive
character is within the range
SCRl
≤
receive character
≤
SCRh.
Table 14. SCdet[x] Settings
SCdet2
SCdet1
SCdet0