I look at Western Design Center 65816 programming manual. The pinout of 6502, 65C02, 65802, and 65816 show IRQB, NMIB, RESB, ABORTB, RWB, etc. What do last letter 'B' mean?

I believe it comes from "bar", IOW, negative logic, meaning low volatage is true and high is false.

The last letter 'B' can't look like "bar". I often call the letter 'N'. The letter 'N' means NOT logical. Sometimes, you can notice the last letter with single quote like " ' "

For example, Reset', NMI', IRQ', etc. It is high to low transition. I often call N_Reset, N_NMI, N_IRQ, etc. Any signal will respond if you pull line to low at least two cycles.

If you prefer low to high transition, MPU will respond during you pull line to high through invert logical.

Please think and how you can say what last letter 'B' stands for. It does not look like invert.

Bryan Parkoff

Different people have different conventions for the negative logic symbol. I personally prefer a slash in front, such as /RES.

So if WDC uses the B as a suffix to denote that, then that is the way it is.

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I went back on three versions of the WDC 65816 datasheet and three 65c02 datasheets, dating back as far as 2000, and they all have the B suffix with no footnotes identifying the "B".

I agree with Garth, that the B stands for "overbar", or "bar" for short. Back in the text-only days of printers, there was not an option to print the "overbar".

That is why the other conventions have come about, such as /RES, !RES, N_RES, etc.

WDC has chosen the B suffix. If you really want to know the exact meaning, try contacting them directly.

EDIT: it just occurred to me that it could also stand for "bubble". You know, the little circle on the output of an inverter symbol. Again, you will have to ask WDC to get the right answer.

Daryl

NMI is edge-sensitive, whereas IRQ is level-sensitive so it doesn't need to see the transition to respond.


They could have made an escape code like for underlining, but they didn't. It was a bit of a pain, but what you could do was underline the area in the line above to get an artificial overbar. OrCAD which I used at work for awhile and had more bugs than an ant hill used the backslash following the signal name, like RST\, so I tend to use that, although I still say what can you expect from a CAD company that after more than two decades still doesn't know how to draw the schematic symbol for a resistor right.