CD2401 Intel, CD2401 Datasheet - Page 84

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

CD2401 — Multi-Protocol Communications Controller
6.5
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Table 18. ETC Byte Sequence
Note: The SglSYN bit (COR3[7]) must be ‘0’ because X.21 mode always requires two SYN characters
X.21 Receive
In receive, the CD2401 validates the steady-state conditions, passing just the change-of-state
information to the CPU. Steady-state conditions validated are:
To be validated a condition must be present for two character times with a stable value on the CTS*
pin (CTS* is used in X.21 as the ‘I’ lead for DTE, or ‘C’ lead for DCE).
For X.21 mode, the SSDE bit (COR3[6]) must be set to enable the detection of the steady-state
conditions; this enables the detection of the all ‘1’s, all ‘0’s, and the alternating ‘1’s and ‘0’s
conditions with a stable value on the CTS* pin. When the SSDE bit is set, the StrpSYN and SCDE
bits (COR3[5:4]) can also be set if required (if SSDE is not set, then the StrpSYN and SCDE bits
have no effect).
for synchronization.
Enable the SSDE and StrpSYN bits to prevent SYN characters from entering the receive data
FIFO. When set, the StrpSYN bit treats SYN characters the same way as steady-state conditions
(that is, when two valid SYN characters are detected, a receive special character interrupt is
generated and the next SYN characters are stripped from the incoming data stream). If the
StrpSYN bit is not set, the SYN character is still used to achieve character synchronization, but all
received SYN characters are passed to the CPU as normal receive data.
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Byte 1
Byte 2
Byte 3
Byte 4
all ‘1’s
all ‘0’s
alternating ‘1’s and ‘0’s
SYN
characters programmed in SCHR1–3.
This byte must be 80 hex to indicate the start of a
command sequence.
This byte indicates the required state of the C lead:
00 = sets the C lead off
01 = sets the C lead on
02–FF= reserved
This byte is the data character to transmit as is with no
parity added.
If parity is required, it must be included in the byte (that
is, to transmit ‘+’ with odd parity, load the value AB).
This byte is a count of the number of times to transmit
the character. If the count is ‘0’, the character is
continuously sent until new data is made available (this
is the normal mode for the steady-state conditions).
In this case, when the count is ‘0’, the CD2401 always
sends the data a minimum of three times, even if new
data is made available before all three characters are
sent.
Datasheet