sane-project-website/old-archive/1998-12/0111.html

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<title>sane-devel: Internet Message Header</title>
<h1>Internet Message Header</h1>
<b>Wolfgang Kaess</b> (<a href="mailto:100346.2055@compuserve.com"><i>100346.2055@compuserve.com</i></a>)<br>
<i>Tue, 8 Dec 1998 16:27:40 -0500</i>
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Alan Knowles &lt;<a href="mailto:alan_k@HK.Super.NET">alan_k@HK.Super.NET</a>&gt; wrote: <br>
<p>
<i>&gt; If someone can point me to a good starter page, on finding out how the &gt;</i><br>
scanner / pc communicate, I could provide some info to help develop a &gt;<br>
driver. I gave up sending polite notes to hp about the lack of info:) <br>
<p>
<i> &gt; </i><br>
 Hello Alan, I got the following from  <br>
 "Scanner Control Language (SCL) and C Language Library for <br>
 Hewlett-Packard Scanners v 8.0" pdf file. <br>
<p>
 Wolfgang Kaess <br>
 Using SANE 0.73 with hp/xhp backend, compiled with IBM VisualAge C++ for OS/2. <br>
 --------------------------------------------------------------------------- <br>
 Parallel Interface Protocol <br>
  Applies ScanJet ScanJet + ScanJet IIp X ScanJet 3p <br>
  to: ScanJet IIc ScanJet IIcx ScanJet 6100C/4c/3c <br>
  ScanJet 4p ScanJet 5p X ScanJet 5100C <br>
<p>
 The HP ScanJet 5100C users an EPST driver/chip to interface a host PC to SCSI   <br>
 Bus device via the host s parallel port. <br>
 This driver/chip converts all the control and logic functions necessary to  <br>
<p>
implement the parallel-to-SCSI interface and <br>
<p>
 vise versa. The EPST device conforms to the  IEEE Std 1284-1994 Standard  <br>
<p>
Signaling Method for a Bi-Directional <br>
<p>
 Parallel Peripheral Interface for Personal Computers , and also works with  <br>
<p>
non-compliant 1284 devices that allow port <br>
<p>
 sharing. <br>
 The parallel interface is a SCSI interface with a parallel wrapper. SCL  <br>
<p>
commands are passed through the same SCSI <br>
<p>
 interface as other scanners but then the signals are passed on to a parallel  <br>
<p>
converter that then sends the commands to <br>
<p>
 the parallel port arbitrator. The arbitrator controls the parallel bus. If  <br>
<p>
the parallel bus is busy, other commands have to <br>
<p>
 wait until the bus is free before they are sent on to the hardware and out to  <br>
<p>
the scanner. If a printer is daisy chained to <br>
<p>
 the scanner, data is passed through to the printer until a scanner specific  <br>
<p>
code is received and then the scanner will <br>
<p>
 block further data from passing through to the printer until the scanner  <br>
<p>
command has completed. Data passed for the <br>
<p>
 scanner is decoded by the parallel EPST chip on board the scanner and  <br>
<p>
converted back to SCSI. Thus no additional <br>
<p>
 commands are needed for parallel operations. <br>
 The HP ScanJet Button Manager is still functional over the parallel interface  <br>
<p>
and is handled by the EPST driver located <br>
<p>
 on the host PC. If the parallel bus is busy and the Button Manager polls the  <br>
<p>
scanner to see if the button has been <br>
<p>
 pressed, the EPST driver reports that the button hasn t been pressed. Once  <br>
<p>
the button is pressed on the scanner its state <br>
<p>
 is stored in the scanner until it is read. When the parallel busy is free,  <br>
<p>
the Button Manager is then allowed to read the <br>
<p>
 scanner to see if the button has been pressed. <br>
 If you are employing SCSI timeouts within your application, your timeouts  <br>
<p>
might need to be extended 5% or more to <br>
<p>
 handle the extra time associated with converting to and from parallel. In  <br>
<p>
most test cases, little or no delay was <br>
<p>
 observed. Test your application to see what, if any, delay is incurred. <br>
<p>
<p>
*** <br>
<p>
<p>
<p>
<pre>
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