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HP LaserJet 5000 HP PCL/PJL reference - Printer Job Language Technical Referen - Page 218

Old Printer Status Readback Responses, Response Data Buffer Overflow

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To keep the I/O interface from timing out, the application can either send data to the printer more frequently than the timeout setting or can cause the printer to use a different setting by sending a PJL JOB command. When I/O-switching printers receive the PJL JOB command, the printer uses an I/O timeout value equal to ten times the TIMEOUT environment variable setting or five minutes, whichever is greater. (If the application sends the PJL JOB command, the application should send a PJL EOJ command at the end of the job.) Old Printer Status Readback Responses Applications need to be designed to handle receiving printer status readback responses that were generated because of an action performed by a different application. For example, a word processing application may send a query to the printer, but because the user turned off the host computer, the application never got a chance to retrieve the response from the printer before the host computer was turned off. When another application, or even the same application at a later time, queries the printer, the first response is the response to the word processing application's query. The currently executing application should accept old printer status readback responses and discard them until the expected response is received. Applications should include unique information as part of the ECHO command, such as the current time and date and a random number, so that the application can resynchronize with printer status readback responses. There is also a chance the PJL ECHO response will never by sent by the printer, due to overflowing of the printer's response data buffer as discussed in the following section. Response Data Buffer Overflow The printer contains a limited amount of memory. It is possible for an application to fill all available printer memory with printer status readback responses that have not yet been sent to the host computer, simply by sending many queries and never accepting the responses from the printer. Also, if an application enables unsolicited status and never accepts responses, the printer's response data buffer can overflow. The printer limits the amount of memory allotted to hold responses, and when that memory is full (and the host has not recently accepted any responses), the printer discards all future responses until the host accepts the currently queued responses in the printer. 11-24 Programming Tips for Using PJL EN

Section	Page
Main Menu	3
Inside This Manual	5
Manual Organization	6
Related Documents	9
Manual Conventions	10
Contents	11
Introduction to PJL	15
What is PJL?	15
The Benefits of PJL	17
Who Should Use PJL?	17
Compatibility With Non-PJL Printers	18
PJL Command Syntax and Format	21
Introduction	21
Syntax Conventions	22
Format of PJLCommands	24
PJL Syntax Rules	25
Types of Variables	27
Processing Invalid Commands	29
Using PJL	31
Introduction	31
Overview of How Commands are Used	31
PJL Job Requirements	33
Some Sample PJLJobs	34
What's Next?	35
Command Groupings by Functionality	36
Kernel Commands	41
Introduction	41
Universal Exit Language (UEL) Command	42
ENTER Command	44
COMMENT Command	46
Methods of Printer Language Switching	47
Job Separation Commands	49
Introduction	49
JOB Command	50
EOJ Command	56
PJL Job Security	58
Password Protection of Default Feature Settings	58
Control Panel Lock	59
Disk Lock	59
Job Cancellation	61
Start of Job Notification	61
End of Job Notification	62
Job Cancellation Unsolicited Status	63
Environment Commands	65
Introduction	65
Print Environments	66
Changing Environment Settings	69
Environment Summary	70
PJL Reset Conditions	72
Key Points to Remember About Environments	74
PJL Environment Variables	75
General PJL Environment Variables	76
Port-Specific Variables (LaserJet4PJ Only)	90
PCL-Specific Variables	91
PostScript-Specific Variables	95
ESC/P-Specific Variables	96
Setting the Printer to a Desired State	98
DEFAULT Command	100
INITIALIZE Command	103
RESET Command	106
SET Command	109
Status Readback Commands	113
Introduction	113
Printer Status Requirements	115
Synchronizing Status Readback Responses	115
Format of Status Readback Responses	116
INQUIRE Command	117
DINQUIRE Command	122
ECHO Command	126
INFO Command	128
USTATUS Command	143
TIMED Variable	152
USTATUSOFF Command	154
Job Recovery	155
Sending the Initial Job	155
After Job Failure	156
Device Attendance Commands	159
Introduction	159
RDYMSG Command	160
OPMSG Command	163
STMSG Command	165
PJL File System Commands	169
Introduction	169
FSAPPEND Command	171
FSDIRLIST Command	173
FSDELETE Command	175
FSDOWNLOAD Command	176
FSINIT Command	177
FSMKDIR Command	178
FSQUERY Command	179
FSUPLOAD Command	181
File System Example	183
Job Management	187
Introduction	187
HP LaserJet 8100 Printer	187
HP LaserJet 8500 Printer	191
Programming Tips for Using PJL	195
Introduction	195
PJL Services	196
Print Data Generators	197
Printer Utilities	199
Spoolers	205
Requesting Printer Status	212
Using Status Readback in a Multi-User System	212
Product-Specific Feature Support	223
Introduction	223
PJL Feature Support	224
PJL Environment Variable Support	228
HP LaserJet IIISi Comments	265
Comments about HP LaserJet Printers	266
LaserJet Printers with Reduced-Function Control Panels	273
Color LaserJet Printer Comments	274
HP DeskJet 1200C and 1600C Printer Family Comments	274
HP LaserJet 5Si/ 5SiMx/5Si Mopier Comments	278
HP LaserJet 5Si Mopier Comments	279
HP LaserJet 4000 and 5000 Series Comments	281
HP LaserJet 1100 Series Comments	283
HP LaserJet 2100 Series Comments	284
HP Color LaserJet 4500 Series Comments	285
HP LaserJet 8000 and 8100 Series Comments	286
HP Color LaserJet 8500 Series Comments	287
PJL Command Summary	289
Programming Examples	295
Introduction	295
PJL Status Codes	301
Status Code Groupings	301
Informational Messages (10xxx) *	302
Background Paper Loading (11xyy)	304
Background Paper Tray Status (12xyy)	306
Output Bin Status (15xxy)	307
PJL Parser Errors (20xxx)	307
PJL Parser Warnings (25xxx)	309
PJL Semantic Errors (27xxx)	310
Auto-Continuable Conditions (30xxx)	311
PJL File System Errors (32xxx)	313
Potential Operator Intervention Conditions (35xxx)	314
Operator Intervention Conditions (40xxx)	316
Foreground Paper Loading (41xyy)	319
Paper Jam Messages (LaserJet 5Si/5SiMx only) (42xyy)	320
Optional (External) Paper Handling Device Messages (43xyy)	322
LaserJet 4000 / 5000 Series Paper Jam Messages (44xyy)	323
Hardware Errors (50xxx)	324
Glossary	327
Index	335
Symbols	335
Numerics	335
A	335
B	335
C	335
D	335
E	336
F	336
H	336
I	336
J	337
K	337
L	337
M	337
N	337
O	337
P	338
Q	339
R	339
S	339
T	339
U	339
V	340

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11-24

Programming Tips for Using PJL

To keep the I/O interface from timing out, the application can either

send data to the printer more frequently than the timeout setting or

can cause the printer to use a different setting by sending a PJL JOB

command. When I/O-switching printers receive the PJL JOB

command, the printer uses an I/O timeout value equal to ten times the

TIMEOUT environment variable setting or five minutes, whichever is

greater. (If the application sends the PJL JOB command, the

application should send a PJL EOJ command at the end of the job.)

Old Printer Status Readback Responses

Applications need to be designed to handle receiving printer status

readback responses that were generated because of an action

performed by a different application. For example, a word processing

application may send a query to the printer, but because the user

turned off the host computer, the application never got a chance to

retrieve the response from the printer before the host computer was

turned off. When another application, or even the same application at

a later time, queries the printer, the first response is the response to

the word processing application's query.

The currently executing application should accept old printer status

readback responses and discard them until the expected response is

received. Applications should include unique information as part of

the ECHO command, such as the current time and date and a

random number, so that the application can resynchronize with printer

status readback responses.

There is also a chance the PJL ECHO response will never by sent by

the printer, due to overflowing of the printer's response data buffer as

discussed in the following section.

Response Data Buffer Overflow

The printer contains a limited amount of memory. It is possible for an

application to fill all available printer memory with printer status

readback responses that have not yet been sent to the host computer,

simply by sending many queries and never accepting the responses

from the printer. Also, if an application enables unsolicited status and

never accepts responses, the printer's response data buffer can

overflow. The printer limits the amount of memory allotted to hold

responses, and when that memory is full (and the host has not

recently accepted any responses), the printer discards all future

responses until the host accepts the currently queued responses in

the printer.