Compuprint 4247-Z03 Programmer Manual - Manual (Page 104)

The printer sends a Negative Acknowledge Reply (NACK) to the host to indicate that an error has
occurred.
The printer can send an ACK or a NACK in response to an ARQ. If an error occurs, the printer can send a
NACK without receiving an ARQ.
The following general rules apply to the printer replies:
v If the printer receives a command requesting acknowledgment and this command also requests specific
printer information, then:
1. The printer sends a positive acknowledgment to the host, and
2. The printer sends the requested information in the data field portion of the Acknowledge Reply.
v If the printer receives a command requesting acknowledgment and this command does not request
specific printer information, then:
1. The printer sends a positive acknowledgment to the host, and
2. The printer does not include any information in the data field portion of the Acknowledge Reply.
v If the printer generates the Acknowledge Reply as a result of detecting an error, then the printer sends a
Negative Acknowledgment (NACK) to the host. Under this condition, the printer also sends to the host
information concerning the error. This error information is in the data field portion of the Acknowledge
Reply.
v The Exception Handling Control command instructs the printer on error processing. For more
information about the Exception Handling Control, see Chapter 4, “IPDS Programming Information,” on
page 99.
v The printer can only return one error per NACK.
v If the printer receives a command requesting an acknowledgment, the printer expects the host to wait
for the acknowledgment before sending further commands. If the printer receives additional commands
from the host within the same transmission after the acknowledgment, the commands are ignored.
IPDS Data
There are various forms of data that the printer uses for creating the output page. These include text,
graphics, bar codes, and images. The printed page can include any combination of this data.
Text data contains lines of character information which the printer places in sequence on the page.
Graphics data contains lines, arcs, markers, and other elements which present a printed picture.
Bar code data is a data type that supports applications requiring precision printing of encoded information
in a form that is recognizable by scanning devices.
Image data contains rectangular arrays of information. The array consists of a sequence of scan lines.
Each scan line consists of picture elements (pels). The image data contains one (dot position) bit per pel.
The text, graphics, bar code, and image data types each have their own unique commands. Chapter 4,
“IPDS Programming Information,” on page 99 contains a detailed description of these commands.
Blocks of graphics, image, or bar code data are presented as a single unit to the printer. The printer
enters the appropriate Block State (graphics block, image block, or bar code block) to create the entire
data group for that block of data.
Page segments and overlays are any combinations of text, graphics, bar codes, and images. The printer
can store these segments and overlays for later use as the page is created. For information about
segments, see “Include Page Segment (IPS)” on page 195. For information about overlays, see “Begin
84 Programmer Manual