HTML version of MCS6500 Microcomputer Family Programming Manual now available

[lbaeza]

Hi team

 

The original MCS6500 Microcomputer Family Programming Manual by MOS Technology has already been scanned some time ago, you can find it here:

 

https://archive.org/details/6500-50a_mcs6500pgmmanjan76

 

I made an HTML version of this book, you can find it here now:

 

https://lbaeza.neocities.org/mcs6500/

 

Feel free to share this link and to make an improved version of this webpage if you want to.

 

Oh, and let me know of any errors you may find.

 

Kind regards,

Luis.

Edited February 6, 2023 by lbaeza
Tag

[sanny]

Nice work!

 

It would be nice to have everything in a single HTML file, though.

 

regards,
chris

[Panther]

This is very nicely done and must have taken quite some time to format.

 

[lbaeza]

Hi

 

Please help me understand this concept: "COLLECTOR OR'd". I'm in the process of translating the full text of this programming manual to spanish language, and I need a hand with this concept.

 

On Chapter 9 "Reset and Interrupt considerations", there's this paragraph:

 

Quote

Up until this point, this discussion has addressed itself to transferring of data into and out of the microprocessor. However, there is a concept that is inherent in the bus discipline that says that whenever an interrupt device capable of generating an interrupt desires to accomplish an interrupt, it performs two acts; first, it sets a bit, usually bit 7, in a register whose primary purpose is to communicate to the microprocessor the status of the device. The interrupting device causes one of perhaps many output lines to be brought low. These collector-or'd outputs are connected together to the IRQ pin on the MCS650X microprocessor.

Google does not help on this one, the only other reference I found for this term is on a Op-Amp datasheet:

 

https://www.digikey.tw/zh/htmldatasheets/production/1775292/0/0/1/ncv5652mutwg.html

 

Quote

Pin 3 is an open collector output that can be connected to a microcontroller to alert the system that a thermal shutdown has occurred. The thermal shutdown circuit has approximately 20°C hysteresis. When the device is in a thermal shutdown condition, the outputs are tri−stated. The same pin can be used for an input as well. It can be open collector OR’d so that the microcontroller can disable the device by driving this pin low.

 

Can you please help me clarify this term?

 

Thanks in advance,

Luis.

[Teapot]

The IRQ input pin activates when the signal goes low. When there are multiple devices that might request an interrupt the model is to use a pull-up resistor on the circuit so its default state is high. And each device's interrupt output uses the open collector model. Which is to connect to ground to signal a low output, but basically disconnect itself to signal a high output. This way any device can request an interrupt by going low without fighting against another device trying to hold the line high (there's only a resistor doing that). It also means multiple devices can request an interrupt without conflict. The 6502 will have to query the devices to handle each of their interrupts but as it does so each device will stop pulling the line low in turn. The IRQ line will stay activated and keep causing interrupts until all the devices have been reset and there's only the resistor left active on the circuit pulling it high.

[lbaeza]

Hi team

 

I found this article on the Victor 9000 Computer: https://www.commodore.ca/wp-content/uploads/2018/11/victor-9000-computer-byte-1982.pdf

 

It includes this description for the IRQ pin:

Quote

Interrupt request. This input should be driven with an open collector driver; it is "collector ORed" with five 6522s and one 6852 and is pulled to +5 volts (V) through a 3.3K-ohm resistor. 

In addition to that, I found this article on 6502 PRIMER: http://wilsonminesco.com/6502primer/IRQconx.html

This article includes this paragraph:

Quote

Most interrupts would come in on the IRQ input.  Many of the 65-family I/O ICs have open-drain interrupt outputs so they can all go to the microprocessor by the same wire.  This is a "wire-OR" logic and you'll need a pull-up resistor to bring the IRQ line high (meaning false) when nothing is pulling it down.  3KΩ is usually recommended in the data books.  3.3K is a standard 5% (and even 10%) value and is close enough. 

 

The graphic shows a pull-up resistor connected to the processor IRQ pin and to 3 switches, and each of these switches belong to each of the devices that may request an interrupt. I am aware of the pull-up resistor concept, I usually use it with multi-game cartridges. With the help of a resistor and a switch to ground, I can make the highest address line either low (GND) or high (+5V).

 

Is this "wire-OR" described here the same as the "collector OR'ed" concept that Teapot explained in this thread?

 

Kind regards,
Luis.

[Teapot]

12 minutes ago, lbaeza said:

Is this "wire-OR" described here the same as the "collector OR'ed" concept that Teapot explained in this thread?

Yes. Different names for the same circuit.

 

I suppose "wire-OR" is more generic so it can be used with no concern about implementing it with collector/emitter or source/drain devices.

[lbaeza]

Just a heads up, the spanish translation for this manual is now available here:

 

https://www.atariware.cl/wiki/Biblioteca/MCS6500

 

Kind regards,

Luis.