CD2401 Intel, CD2401 Datasheet - Page 86

• Manufacturer Part Number: CD2401
• Description: Multi-protocol Communications Controller
• Manufacturer: Intel

CD2401 — Multi-Protocol Communications Controller
6.6.2
86
Table 19. Byte Format — ETC Bit Set
Note: This feature is not available in revisions prior to revision ‘H’.
Note: Strip SYN and SCDE are functional only if the SSDE is set.
First, the idle character can be supplied as normal data; the drawback is that host intervention is
required to either fill the FIFO or supply a new DMA buffer periodically while there is no real data
to send. The second method is to use the ETC to repeat the required data pattern until transmit data
is available. The ETC command functions as shown in
When an 80 hex character is encountered in the transmit data, it and the following three characters
are treated as a special command. The byte format is:
To idle in mark with the RTS* line off, write the command ‘80 00 FF 00’. To send the character
‘80’ while the ETC command is enabled and the RTS* pins asserted, write the sequence
‘80 01 80 01’.
Extended X.21 Receive
In Receive mode, the SYN character can be programmed in COR6 to be any required value. When
the channel is initialized, COR6 is initially set to the value ‘16’ by the internal code; host software
can reprogram COR6 to the required SYN value after channel initialization is complete. If a parity
mode is enabled, the parity bit should not be set in COR6. Synchronization can be achieved with
either a single- or double-SYN pattern; this is controlled by the SglSYN bit (COR3[7]).
Since the channel does not look for an end-of-frame delimiter, the host must determine when to end
the frame and/or to terminate the buffer (if DMA is used) with software. It must also detect when to
start another frame.
Extended X.21 mode still passes received data to host before and/or after it receives the SYN
character(s). The host can discard all the junk characters before the SYN character(s) whenever the
device detects SYN character(s) and generates an interrupt.
If the SSDE bit (COR3[4]) is not set, Extended X.21 mode does not strip SYN characters and
special characters from the incoming data stream.
Byte 1
Byte 2
Byte 3
Byte 4
This byte must be equal to 80 hex to start a command
sequence.
This byte indicates the required state of the RTS* pin.
00 = the RTS* pin is set inactive (high)
01 = the RTS* pin is set active (low)
02–FF= reserved
This byte is the required character for transmission. It
is sent as an 8-bit character without parity (any
required parity value is included by the host).
This byte is the number of times the above character
should be sent. If set to ‘0’, the character is sent until
new data is supplied.
In this case, the CD2401 always sends the data a
minimum of three times, even if new data is made
available before all three characters are sent.
Table 19
(COR2[5] is set).
Datasheet