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#gpib

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Dirk Wouters<p>Neue Hauptplatine für das Commodore 1541-Diskettenlaufwerk, Teil II </p><p>Hier nun der versprochene 2. Teil über eine neue Systemplatine für das Floppy-Laufwerk VC1541 von Commodore. Ein komplettes Redesign und die Zusammenführung verschiedener Projekte zu einem neuen Controller…</p><p>#1541 <a href="https://mastodon.social/tags/C128" class="mention hashtag" rel="nofollow noopener noreferrer" target="_blank">#<span>C128</span></a> <a href="https://mastodon.social/tags/c64" class="mention hashtag" rel="nofollow noopener noreferrer" target="_blank">#<span>c64</span></a> <a href="https://mastodon.social/tags/commodore" class="mention hashtag" rel="nofollow noopener noreferrer" target="_blank">#<span>commodore</span></a> <a href="https://mastodon.social/tags/CPLD" class="mention hashtag" rel="nofollow noopener noreferrer" target="_blank">#<span>CPLD</span></a> <a href="https://mastodon.social/tags/Disk" class="mention hashtag" rel="nofollow noopener noreferrer" target="_blank">#<span>Disk</span></a> <a href="https://mastodon.social/tags/DolphinDOS" class="mention hashtag" rel="nofollow noopener noreferrer" target="_blank">#<span>DolphinDOS</span></a> <a href="https://mastodon.social/tags/Ersatz" class="mention hashtag" rel="nofollow noopener noreferrer" target="_blank">#<span>Ersatz</span></a> <a href="https://mastodon.social/tags/Erweitert" class="mention hashtag" rel="nofollow noopener noreferrer" target="_blank">#<span>Erweitert</span></a> <a href="https://mastodon.social/tags/Generation" class="mention hashtag" rel="nofollow noopener noreferrer" target="_blank">#<span>Generation</span></a> <a href="https://mastodon.social/tags/GPIB" class="mention hashtag" rel="nofollow noopener noreferrer" target="_blank">#<span>GPIB</span></a> <a href="https://mastodon.social/tags/IEEE488" class="mention hashtag" rel="nofollow noopener noreferrer" target="_blank">#<span>IEEE488</span></a> <a href="https://mastodon.social/tags/Laufwerk" class="mention hashtag" rel="nofollow noopener noreferrer" target="_blank">#<span>Laufwerk</span></a> <a href="https://mastodon.social/tags/Mainboard" class="mention hashtag" rel="nofollow noopener noreferrer" target="_blank">#<span>Mainboard</span></a> <a href="https://mastodon.social/tags/Neu" class="mention hashtag" rel="nofollow noopener noreferrer" target="_blank">#<span>Neu</span></a> <a href="https://mastodon.social/tags/PCB" class="mention hashtag" rel="nofollow noopener noreferrer" target="_blank">#<span>PCB</span></a> <a href="https://mastodon.social/tags/SpeedDOS" class="mention hashtag" rel="nofollow noopener noreferrer" target="_blank">#<span>SpeedDOS</span></a> <a href="https://mastodon.social/tags/VC1541" class="mention hashtag" rel="nofollow noopener noreferrer" target="_blank">#<span>VC1541</span></a> <a href="https://mastodon.social/tags/Weiter" class="mention hashtag" rel="nofollow noopener noreferrer" target="_blank">#<span>Weiter</span></a> <a href="https://mastodon.social/tags/Xilinx" class="mention hashtag" rel="nofollow noopener noreferrer" target="_blank">#<span>Xilinx</span></a></p><p><a href="https://dirkwouters.de/neue-hauptplatine-fuer-das-commodore-1541-diskettenlaufwerk-teil-ii/" rel="nofollow noopener noreferrer" translate="no" target="_blank"><span class="invisible">https://</span><span class="ellipsis">dirkwouters.de/neue-hauptplati</span><span class="invisible">ne-fuer-das-commodore-1541-diskettenlaufwerk-teil-ii/</span></a></p>
Retrograde<p>Implemented (in 6502 assembler) the <a href="https://oldbytes.space/tags/GPIB" class="mention hashtag" rel="nofollow noopener noreferrer" target="_blank">#<span>GPIB</span></a> code for sending and receiving a byte using 3-way handshake, through the IEC64 cartridge. Maybe...</p>
Retrograde<p>Michael Steil has documented the official Commodore IEEE-488 interface over at <a href="https://www.pagetable.com/?p=1303" rel="nofollow noopener noreferrer" translate="no" target="_blank"><span class="invisible">https://www.</span><span class="">pagetable.com/?p=1303</span><span class="invisible"></span></a></p><p>That one seems a little more kosher than the IEC64 open source hardware version I have here. Fx there are no 75160+75161 bus transceivers on this cartridge, otherwise ubiquitous on <a href="https://oldbytes.space/tags/GPIB" class="mention hashtag" rel="nofollow noopener noreferrer" target="_blank">#<span>GPIB</span></a> boards so it's not going to be able to work at the cable length specified in IEEE-488 but is probably fine for this particular use.</p><p>It's basically just an I/O expander (an MC6821 PIA) mapped to the /IO1 slot in the <a href="https://oldbytes.space/tags/C64" class="mention hashtag" rel="nofollow noopener noreferrer" target="_blank">#<span>C64</span></a> memory map ($DE00-$DEFF) and a replacement kernal ROM with patched I/O routines to support this interface. I'll be talking to the PIA directly instead.</p><p>The interrupt facility of the 6821 is not connected to the C64 bus, so it's plain old polled I/O.</p>
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Retrograde

#GPIB (what ultimately became IEEE-488) originated with HP as an instrument control interface in the 1960s, but Commodore adopted it for its earliest peripherals (of course, this being Commodore, not using the standard connector, but a cheaper edge connector).

It was used in the PET era, but the very first disk drive I had for my #C64 was actually using an IEEE-488 cartridge (might have been a 2031 drive, but I have no record of it).

Even though with its parallel nature, it was way faster with regular kernal I/O than Commodore's later serialised version of the interface, I didn't like it at all at the time because so many games and demos blindly assumed to find a 1541 connected and did not work with it.

Sure wish I'd held on to that now... 😢​

#RetroComputing
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