CD2481 Datasheet, PDF (86/222 Pages) Intel Corporation – Programmable Four-Channel Communications Controller

CD2481 — Programmable Four-Channel Communications Controller
Note that if automatic out-of-band flow control is implemented, the activity of DTR and DSR pins
do not implement the function assigned to those signal names by the signalling conventions of the
CCITT and other standards organization. These names would only apply to these pins if they are
under program control and not under automatic CD2481 control. In fact, the “DTR” function
enables the modem to go on- and off-line, depending on the state of the pin. If automatic control is
used, then DTR would go inactive when the receive FIFO reached the programmed threshold thus
causing the modem to drop the connection (carrier) to the remote, which would not be the correct
function based on the state of the receive FIFO.
7.5.4
Line Break Detection and Generation
A line break on the receiver occurs when the input at the receive data (RxD) pin is all zeros (low)
for at least one full character time. This is indicated when the Break bit (RISRl[0]) is set to ‘1’.
Line break generation out of the transmitter is possible when the Embedded Transmit Command
(ETC) bit {COR2[5]) is set to 1. A line break is generated when the output at the transmit data
(TxD) pin is all zeroes (low) for at least one full character time.
Line breaks may be transmitted by embedding certain sequences in the data stream, as defined in
the table below.These sequences are valid for transmitting breaks only if ETC is set to ‘1’. The
embedded sequences to transmit a break are listed below.
Sequence
00h-81h
00h-82h-xxh
00h-83h
00h-00h
Function
Send BREAK – Send a line break for at least one character time.
Insert Delay – To increase the break generation beyond one character time, the
Insert Delay sequence may be used. The inserted delay will be xx, where xx is a
binary number. The delay will be xx times the 'tick' set by the Timer Period register
(TPR). The minimum period of TPR should be 1 millisecond. If the Insert Delay
sequence is not preceded by a Send BREAK sequence, then there will be an
inserted delay of all 1's (high) on the output for duration xx.
Stop BREAK – This must follow the Send BREAK sequence, or the Insert Delay
sequence.
Send NUL – If the user needs to send a NUL character, and ETC = 1, the user may
embed 00h-00h to send one NUL character. If there are less than 8-bits per
character, the user may also send a NUL character by 'sending' an 80h.
Note: In addition to Insert Delay, a 'break' may also be increased beyond one full character by
transmitting me than one 'Send BREAK' sequence at a time.
7.5.5
Special Character Transmission
Selected special characters may be sent preemptively by setting the SndSpc bit (STCR[3]. The
CD2481 channel acknowledges the command by clearing the STCR. Along with the SndSpc bit,
the host needs to set-up the three SSPC bits (STCR[2:0], also in the STCR to select which character
is to be sent.
When the host commands a special character transmission, the channel will complete transmitting
any characters in the Transmit Shift register and Transmit Holding register, and then transmit the
special character sequence. Any other characters awaiting transmission in the FIFO or through
DMA will be transmitted after the special character.
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Datasheet