Gdd Initial Graphics Defaults Self-Describing Instructions; Position-And-Trim Mapping - IBM 6400 Programmer's Reference Manual

Graphics Command Set
Figure 21. Position-and-Trim Mapping

GDD Initial Graphics Defaults Self-Describing Instructions

This portion of the Graphics Data Descriptor structured field contains zero or
more self-describing instructions that set the drawing defaults for the graphics
picture. The general format of a self-describing instruction is:
21 Length Set Mask Default Data
The first byte, 21, indicates that the following parameter is a Set Current Defaults
instruction.
The Length byte is the length of the following data. If this value equals 4, the
printer uses the standard default values.
The Set byte indicates the type of attribute or parameter this instruction is
specifying.
The bits 0 through 15 in the Mask bytes correspond to attribute items within the
indicated set. The individual set descriptions explain the meanings of these bits.
When a mask bit equals one, the value of the default byte selects one of two
options. See the default byte description for details. When a mask bit equals
zero, the default does not change and the data does not include the value for the
corresponding attribute.
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Chapter 3. IPDS Commands Reference