Difference between revisions of "New Bus Expander by Wilco"

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(Created page with "Bus Expander ==How to use it== I want to give you some recommendations of use for the Bus Expander on its second version, but if you find...")
 
(How to use it)
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[[File:BusExpander.jpg|thumb|400px|Bus Expander]]
 
[[File:BusExpander.jpg|thumb|400px|Bus Expander]]
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==The original plan==
 +
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==The card==
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This card is a modern copy of the Hungarian made Bus Expander[http://www.ep128.hu/Ep_Hardware/Ep_Buszkiterjeszto.htm] designed long ago by Gyula Mészáros. He was an active Enterprise hardware designer in an era when Hungary was behind the Iron Curtain, almost a hero when information and electronic components where very difficult to reach.
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Actually we know that Enterprise Computers LTD. also reached to full design their original Bus Expander[http://enterprise.iko.hu/schematics/A3PER-12_Enterprise_64-128_Expansion_Motherboard_Schematic.jpg]. On the information about it that has surfaced, we can see that the slots had eight additional pins(74) than the computer expansion connector(66), three of them used to codify the Z80 ports and the memory segments used by the plugged card, to not collide with the ports and memory segments used by the other slots in the Bus Expander. A similar technique was used on the MSX computer cartridge slots. All the important signal lines where  buffered to protect the computer internal circuits and, as a curiosity, the Colour Input Bus was only connected to the first slot, the Stereo Sound Input only to the first and second. Only the +9v line from the computer was used, being other voltages isolated. The +5v, +12v and -12v where provided by an "inbuilt power supply" on the Bus Expander.
 +
 +
Mészáros source of information to make his Bus Expander was  only extracted from the construction of the original System Bus Bridge, in reality a single slot Bus Expander, a cheap solution to connect the EXDOS module, the only full expansion that was commercialised before the end of the company. Of course his design lacked some of the characteristics of the original design, like the extra coded pins or the +12v and -12v lines. The signal buses where also buffered slightly different, and the +5v line was not provided so, every card plugged had to create its own +5v voltage, which was logical, with the consumption hungry components in that time.
 +
 +
As a result of that design, all the slots had the same priority, leaving to the extension card designer the obligation to know which resources had been used previously on other cards, to not to collide with them.
 +
 +
We can think that the original design was superior, but practically the Mészáros' system is what has worked all these years as a standard. It is too late to take over the original design and, on the other side, the de facto "standard" has also some benefits, like no restrictions on the number of segments or Z80 ports that can be used on a slot.
 +
 +
Curiously, the Vidoton or TVcomputer, the Hungarian brother of the Enterprise, was created with a different system of coded slots integrated on the main board[http://tvc.homeserver.hu/doc/tervrajzok/TVC_HBA2_rajzok.pdf].
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==How to use it==
 
==How to use it==
 
I want to give you some recommendations of use for the Bus Expander on its second version, but if you find difficult to understand this, please ask Zozo about how to prepare the Bus Expander to work with your classic card expansions.
 
I want to give you some recommendations of use for the Bus Expander on its second version, but if you find difficult to understand this, please ask Zozo about how to prepare the Bus Expander to work with your classic card expansions.
  
This card is a modern copy of the Hungarian made Bus Expander designed long ago by Gyula Mészáros, but with a particularity: by default the cards plugged in the slots will feed its +5v from the 7805 regulator fitted in the Bus Expander from pins 4A/B of the connector.
+
This card has a particularity over Mészáros' design: by default the cards plugged in the slots will feed its +5v from the 7805 regulator fitted in the Bus Expander from pins 4A/B of the connector.
  
 
But all the classic Hungarian expansion cards have its own 7805 regulator and they will not work directly, so you have to do a modification on the bottom side of the Bus Expander. The slots come unconnected from +9v on the 33A/B pins of the connector, but there are a selector at the bottom side on every slot to permit this only joining two cooper pads with a drop of tin. Then, the modified slot will be only used for a classic expansion.
 
But all the classic Hungarian expansion cards have its own 7805 regulator and they will not work directly, so you have to do a modification on the bottom side of the Bus Expander. The slots come unconnected from +9v on the 33A/B pins of the connector, but there are a selector at the bottom side on every slot to permit this only joining two cooper pads with a drop of tin. Then, the modified slot will be only used for a classic expansion.

Revision as of 13:59, 22 January 2019

Bus Expander

The original plan

The card

This card is a modern copy of the Hungarian made Bus Expander[1] designed long ago by Gyula Mészáros. He was an active Enterprise hardware designer in an era when Hungary was behind the Iron Curtain, almost a hero when information and electronic components where very difficult to reach. Actually we know that Enterprise Computers LTD. also reached to full design their original Bus Expander[2]. On the information about it that has surfaced, we can see that the slots had eight additional pins(74) than the computer expansion connector(66), three of them used to codify the Z80 ports and the memory segments used by the plugged card, to not collide with the ports and memory segments used by the other slots in the Bus Expander. A similar technique was used on the MSX computer cartridge slots. All the important signal lines where buffered to protect the computer internal circuits and, as a curiosity, the Colour Input Bus was only connected to the first slot, the Stereo Sound Input only to the first and second. Only the +9v line from the computer was used, being other voltages isolated. The +5v, +12v and -12v where provided by an "inbuilt power supply" on the Bus Expander.

Mészáros source of information to make his Bus Expander was only extracted from the construction of the original System Bus Bridge, in reality a single slot Bus Expander, a cheap solution to connect the EXDOS module, the only full expansion that was commercialised before the end of the company. Of course his design lacked some of the characteristics of the original design, like the extra coded pins or the +12v and -12v lines. The signal buses where also buffered slightly different, and the +5v line was not provided so, every card plugged had to create its own +5v voltage, which was logical, with the consumption hungry components in that time.

As a result of that design, all the slots had the same priority, leaving to the extension card designer the obligation to know which resources had been used previously on other cards, to not to collide with them.

We can think that the original design was superior, but practically the Mészáros' system is what has worked all these years as a standard. It is too late to take over the original design and, on the other side, the de facto "standard" has also some benefits, like no restrictions on the number of segments or Z80 ports that can be used on a slot.

Curiously, the Vidoton or TVcomputer, the Hungarian brother of the Enterprise, was created with a different system of coded slots integrated on the main board[3].


How to use it

I want to give you some recommendations of use for the Bus Expander on its second version, but if you find difficult to understand this, please ask Zozo about how to prepare the Bus Expander to work with your classic card expansions.

This card has a particularity over Mészáros' design: by default the cards plugged in the slots will feed its +5v from the 7805 regulator fitted in the Bus Expander from pins 4A/B of the connector.

But all the classic Hungarian expansion cards have its own 7805 regulator and they will not work directly, so you have to do a modification on the bottom side of the Bus Expander. The slots come unconnected from +9v on the 33A/B pins of the connector, but there are a selector at the bottom side on every slot to permit this only joining two cooper pads with a drop of tin. Then, the modified slot will be only used for a classic expansion.

Bus Expander bottom side

Previously, you have to solder a DIL row of pins on the EDGE male connector of your classic card expansion. I will distribute the Bus Expansions only fitted with DIL connectors. But there are on the card holes to solder EDGE connectors, not provided by me.

The Enterprise power supply comes on +9v 2Amp or 1,3Amp variants, so, when all the equipment is connected, if you experience undulations on the screen, probably you need to connect a secondary power supply on the Bus Extension auxiliary power connector.

Also, every 7805 regulator can feed up to 1Amp of current, and this can be insufficient to feed the three slots when all of them being populated. This doesn't applies to slots modified for classic expansions as they produce its own +5v. The rear connector also doesn't count, it only feeds from +9v.

To overcome this I recommend to substitute the 7805 regulator that comes installed (the chip with screw and heat sink) with a 2Amp TracoPower regulator(I don`t recommend the 1Amp variant, of similar price): https://hu.rs-online.com/web/p/kapcsolas-szabalyozo-es-kiegeszito/1616642/

R9068480-01.jpg

The chip has the same pinout than the 7805, and I have used it for decades on my Enterprises without problems. This chip works at ambient temperature, is more energy efficient and doesn't burn your fingers...

On this second version of the Bus Expander, holes have been added to fit an array of 4,7K pull ups to the Data bus, to overcome some problems of shadow segments when a Ram expansion or Turbo mode are fitted to the computer. You can see the pads zone near the expansion connector.

Pull-up array holes