ijpds formats.book - Kodak

Chapter 4. Record Formats
Character Definition with Metrics (CDM)
Character Definition with Metrics (CDM)
CDM records, which are interchangeable with CCD records, follow an
SFM or FDM record and define each character in the font. The CDMs
contain the bitmap patterns for the characters. Up to 256 characters can
be defined for each FDM and up to 65,536 characters for an SFM.
Usually, there is one CDM for each character. However, in some fonts, a
continuation CDM is used to divide a character bitmap into two or more
records if it is necessary to limit the size of the records (because of block
length restrictions or other reasons). The character bitmap can be broken
only at the end of a row. When continuation CDMs are used, all fields up
to the bitmap pattern field must be the same in each CDM for the
character except for the continuation bit in the last CDM.
When an SFM or FDM is received, the printer defines null and default
characters in the following manner. When an SFM or FDM is first
processed by the printer, all characters in the font are set as null
characters. If the first CDM received has the default bit set, then the
character in this record is used as the default character. The default
character is used for all undefined characters in the font, including
character 00. Subsequent CDMs then redefine the characters for their
respective character identifiers. If the first CDM does not have the default
character bit set, then all characters remain null until redefined by
subsequent CDMs.
A null character has zero width and height, zero X and Y escapement,
and takes no space when printed.
Note: An example of FDM and CDM coding is shown in Appendix B.
Byte Position Bytes Field Name Description
1-2 2 Record Length The length of this record, in binary, including the record length
field. For example, hex 00 8C specifies a record length of 140
bytes.
3 1 Cyclic Record Count A binary cyclic record count using modulo 256. Each record in the
job is counted, starting with hex 01 for the first record. The 255th
record is hex FF and the 256th record is hex 00. This count is used
to verify record sequence.
4 1 Control Code A binary code that identifies the record type. A value of hex 30
identifies the CDM record.
5-6 2 Character Identifier A binary code that identifies the character defined in this record.
This is the code that must be used in the input data to access this
character for printing. The range is 0 - 255 for regular font
characters or 0 through 65,535 for super font characters.
If the default bit in byte 7 is set, this field is ignored.
7 1 Options Two bits in this field are used to specify two character definition
record options. Bit assignments are as follows.
Bit 0 (hex 80 bit)=Default Character bit.
Bit 1 (hex 40 bit)=Continuation bit.
If the default bit is set, this character must be the first one defined
in the font.
8 1 Reserved This field is not used and must contain all binary zeroes.
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