Cypress CYV15G0404DXB manual Use of the Tables for Generating Transmission Characters, DIN or QOUT

CYV15G0404DXB

mission of any transmission character, the transmitter selects the proper version of the transmission character based on the current running disparity value, and the transmitter calculates a new value for its running disparity based on the contents of the transmitted character. Special character codes C1.7 and C2.7 can be used to force the transmission of a specific special character with a specific running disparity as required for some special sequences in X3.230.

After powering on, the receiver may assume either a positive or negative value for its initial running disparity. Upon reception of any transmission character, the receiver decides whether the transmission character is valid or invalid according to the following rules and tables and calculates a new value for its running disparity based on the contents of the received character.

The following rules for running disparity are used to calculate the new running disparity value for transmission characters that have been transmitted and received.

Running disparity for a transmission character is calculated from subblocks, where the first six bits (abcdei) form one subblock and the second four bits (fghj) form the other subblock. Running disparity at the beginning of the 6-bit subblock is the running disparity at the end of the previous transmission character. running disparity at the beginning of the 4-bit subblock is the running disparity at the end of the 6-bit subblock. Running disparity at the end of the transmission character is the running disparity at the end of the 4-bit subblock.

Running disparity for the subblocks is calculated as follows:

1.Running disparity at the end of any subblock is positive if the subblock contains more ones than zeros. It is also positive at the end of the 6-bit subblock if the 6-bit subblock is 000111, and it is positive at the end of the 4-bit subblock if the 4-bit subblock is 0011.

2.Running disparity at the end of any subblock is negative if the subblock contains more zeros than ones. It is also negative at the end of the 6-bit subblock if the 6-bit subblock is 111000, and it is negative at the end of the 4-bit subblock if the 4-bit subblock is 1100.

3.Otherwise, running disparity at the end of the subblock is the same as at the beginning of the subblock.

Use of the Tables for Generating Transmission Characters

The appropriate entry in Table 14 for the valid data byte or Table 15 for Special Character byte identify which transmission character is generated. The current value of the transmitter’s running disparity is used to select the transmission character from its corresponding column. For each transmission character

Table 13. Code Violations Resulting from Prior Errors

transmitted, a new value of the running disparity is calculated. This new value is used as the transmitter’s current running disparity for the next valid data byte or Special Character byte encoded and transmitted. Table 12 shows naming notations and examples of valid transmission characters.

Use of the Tables for Checking the Validity of Received Transmission Characters

The column corresponding to the current value of the receiver’s running disparity is searched for the received transmission character. If the received transmission character is found in the proper column, then the transmission character is valid and the associated data byte or special character code is determined (decoded). If the received transmission character is not found in that column, then the transmission character is invalid. This is a code violation. Independent of the transmission character’s validity, the received transmission character is used to calculate a new value of running disparity. The new value is used as the receiver’s current running disparity for the next received trans- mission character.

Table 12. Valid Transmission Characters

Data

Byte Name	DIN or QOUT		Hex Value
	765	43210
D0.0	000	00000	00
D1.0	000	00001	01
D2.0	000	00010	02
.	.	.	.
.	.	.	.
D5.2	010	00101	45
.	.	.	.
.	.	.	.
D30.7	111	11110	FE
D31.7	111	11111	FF

Detection of a code violation does not necessarily show that the transmission character in which the code violation was detected is in error. Code violations may result from a prior error that altered the running disparity of the bit stream which did not result in a detectable error at the transmission character in which the error occurred. Table 12 shows an example of this behavior.

	RD	Character	RD	Character	RD	Character	RD
Transmitted data character	–	D21.1	–	D10.2	–	D23.5	+
Transmitted bit stream	–	101010 1001	–	010101 0101	–	111010 1010	+
Bit stream after error	–	101010 1011	+	010101 0101	+	111010 1010	+
Decoded data character	–	D21.0	+	D10.2	+	Code Violation	+

Document #: 38-02097 Rev. *B Page 37 of 44

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