Compaq 5525B/31/32 manual Programmable VFC, Special VFC Considerations

Programmable VFC

Programmable VFC

Programmable VFC allows the user to specify paper movement information other than the standard VFC definitions shown in Table 7. VFC information is stored in the memory (RAM) table just as the standard VFC is, only the bytes of information are loaded into RAM using the following escape sequence:

ESC&l[byte count]W[VFC data]

The byte count parameter specifies the number (in decimal 0 - 255) of VFC data bytes to expect immediately following the termination of the escape sequence.

NOTE: An even byte count must be indicated. If an odd byte count is indicated, the VFC table in RAM will not be overwritten and the data bytes following the ESC sequence will be read and discarded.

VFC data is the binary data which is loaded into the VFC table in RAM. These 8-bit bytes are sent in the following order following the ESC sequence terminator: the most significant byte of the first word followed by the least significant byte of the first word, followed by the most significant byte of the second word, etc. The most significant bit of each word is channel 16 and the least significant bit of each word is channel 1.

VFC Data = (MS byte) (LS byte) (MS byte) (LS byte) . . .

(word 1 = line 1) (word 2 = line 2) . . .

Once the VFC has been loaded into the RAM table, the VFC channels are selected using the ESC&l[0 through 16]V sequence in the same manner as the standard VFC. The standard and programmable VFC both use the same table in RAM. Resetting the printer causes the standard VFC to be recalculated using the current page and text (form) length and a new table to be overwritten in RAM. The VFC table is also recalculated when the line spacing, text length, or page length changes.

NOTE: If the I/O is configured for 7 bit data, channels 8 and 16 cannot be downloaded with confidence since the eighth bit is used for the communication protocol. Selecting channels 8 or 16 for 7 bit data is not recommended.

Special VFC Considerations

Before loading a VFC table, it is recommended that a VFC select of channel 0 be performed. This will bring the printer to the top of the physical page.

When a programmed VFC is loaded into RAM, the logical page length is automatically calculated using the following formula:

Logical Page Length (in number of lines) = byte count /2

The example on page 35 shows a VFC table which uses “standard” VFC definitions and also illustrates a programmable VFC.

Example: Defining a 3.5 inch form at six lines per inch. 1 inch = 6 lines x 3.5 inches = 21 lines

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