Easier Way to Understand Configuring the FDC+ board ...

[Walt Perko]

Hi, 

I was thinking, there should be an easier way to figure out how to configure the FDC+ board.

For beginner people only using the FDC+ to connect to the FDC+ Serial Drive Server ... as for me with dyslexia and failing eyesight, reading the manual and getting everything figured out is very difficult whereas little tables showing DIP Switch Configurations can make life easier and a computer setup much faster.  

Even now I'm not sure how to Disable the EPROM to only have RAM so the board doesn't conflict with other boards with ROMs in the computer.  Is the EPROM completely removed from the S-100 bus when the EN switch is DN?  

S3 DIP Switch ... do we need to select a specific drive?  

My settings have always been:  00000111 or Serial Drive as Altair 8" Drive

But would S3 switch be something different to connect to the ESP32 FDC+ WiFi module with three 8MB floppies and one 360KB floppy?  

With Multi-User CP/M 2.2b it's nice to have tons of floppy space for various projects, sorting every program for the Altair 8800 into types on each USER x drive ... e.g., Utilities, Games, etc.  

S1 DIP Switch RAM Start Address:  00000000 starts at 0000H so the board is 64K RAM

This is where it would be nice if the manual had a table showing addresses and switch settings:  

RAM  EN  15    14    13    12     11    10

 DN    DN   DN   DN   DN   DN   DN   DN  =  Start Address 0000H ... 

RAM and EN = DN = RAM Enabled

S2 DIP Switch EPROM Setting:   11110000 

Again it would be nice if the manual had a table showing addresses and switch settings:  

EN   14   13   12   11    10     9      8

UP   UP   UP  UP  DN   DN   DN   DN  = E000H

UP   UP   DN  UP  DN   DN   DN   DN  = A000H

UP   UP   UP  DN  DN   DN   DN   DN  = C000H

UP   UP   DN  DN  DN   DN   DN   DN  = 8000H

For the even more advanced uses ... 

S4 DIP Switch Interrupt Select:  00000000

.

[Patrick Linstruth]

Would something like this help?

[Walt Perko]

Hi, 

Yeah, that's an easier guide for non-engineers to learn how to use the board.  

I have three things I don't like about the document.  

1st. is:  U and D are used to identify components on boards, but UP and DN tend to be obvious positions of a switch.  

2nd. is from Paragraph 2  Important Note on RAM and PROM Interaction:  It seems to imply that if people set the PROM address to FFOO they will have maximum RAM for their programs, but it doesn't say they will be cutting out some of the PROM utilities.  

3rd. issue is:  What is X/U and X/D?  in the chart for  "Table: Common PROM Starting Page Examples (S2)"  

.

[Patrick Linstruth]

On Mar 29, 2026, at 11:56 AM, Walt Perko <r4r...@gmail.com> wrote:

Hi, 

Yeah, that's an easier guide for non-engineers to learn how to use the board.  

I have three things I don't like about the document.  

1st. is:  U and D are used to identify components on boards, but UP and DN tend to be obvious positions of a switch.

I will make that change, although it tells you exactly what U and D mean:

To set a switch to logical 1, move the actuator Up (U) toward the top of the PCB. To set it to logical 0, move the actuator Down (D) toward the bottom of the PCB. Unused switches in any bank may be left in either position.

  

2nd. is from Paragraph 2  Important Note on RAM and PROM Interaction:  It seems to imply that if people set the PROM address to FFOO they will have maximum RAM for their programs, but it doesn't say they will be cutting out some of the PROM utilities.  

It doesn’t imply that at all. It is very clear that the “starting" PROM address also provides the “ending" RAM address. If you tell the FDC+ to start PROM at F800, then RAM ends at F7FF. Period. There aren’t separate PROM and RAM starting and ending addresses. If someone sets the PROM starting address to FF00 and their PROM utilities are located below that address, F800 for example, then it’s obvious that they won’t have access to those PROM utilities because they set the start address above them. It also doesn’t mean they if they flip the right switches they will automatically have all that RAM available for programs. It would depend on which programs, how the program determines available RAM, etc. Assuming they are running something like CP/M, they would still need a CP/M configured to use that amount of RAM.

Also, the document includes the following:

Important Note on RAM and PROM Interaction

The ending address of the on-board RAM is determined by the PROM starting address set on S2, even if the PROM is disabled. If only RAM is needed without the PROM, the PROM start address is still used to determine the RAM end address (even when the PROM enable switch is set to disable the PROM). The maximum PROM starting address is FF00h, so without the optional 64K RAM modification, the on-board RAM cannot extend above FF00h (the top 256 bytes remain unavailable). See FDC+ manual section 2.2.1.

3rd. issue is:  What is X/U and X/D?  in the chart for  "Table: Common PROM Starting Page Examples (S2)"  

Above that column it is says (Rev B/C) X/U and X/D means that the option isn’t supported on the Rev B board and Up or Down on a Rev C board will make it a 1 or 0, which should be obvious to the person with a Rev B board because their board won’t have stenciles for A14 or A13. A15 is always 1 on both Rev B and C. A14 and A13 are always 1 on Rev B. Because A15-A13 are always 1 on a Rev B board, it is not possible to select starting PROM address of C000.

Revision B: A15–A13 are fixed as 1 (PROM fixed in E000h–FFFFh range). The two leftmost switch positions (if present) are unused.

C000

(Rev C Only)

Always verify your board revision (B or C) as it affects PROM/RAM address behavior.

If someone were to provide documentation where the reader only had to look at a table and not read or comprehend any clarifying documentation, it would be 50 pages long and there would still be at least one person that didn’t think it was simple or clear enough because the answer to most configuration questions is, “it depends."

I’ve attached the word document with some of your changes. Feel free to modify it and make it more simple.

[Walt Perko]

Hi, 

Patrick ... you are not dyslexic.  Hence looking at the charts U and D look like barcodes, not letters, but UP and DN are very distinct.  

What I was trying to get at on the 2nd EPROM addressing was that the paragraph doesn't tell people they're cutting out what they might need from the EPROM, but telling them how to get maximum RAM in the system.  IF somebody just sets the DIP switches for maximum RAM and tries to BOOT F800 they cannot get into the monitor.  

I still say X/1 isn't defined.  What does the X actually mean?  Neither B or C boards?  

I see:  

Revision B: A15–A13 are fixed as 1 (PROM fixed in E000h–FFFFh range). The two leftmost switch positions (if present) are unused. 

Revision C: A15 is fixed as 1; A14 and A13 are typically set to 1 for standard configurations (allowing starts at 8000h, A000h, C000h, or E000h, with content repeating to FFFFh).  

but not a definition for X ... 

.

[Patrick Linstruth]

The switches set the PROM starting address. Do we really need to explain that if your PROM monitor is at F800 and you set the PROM STARTING ADDRESS to FF00, that you won’t be able to access your PROM code at F800?

I provided the Word document. Make all the revisions you think would help.

Probably the thing to do is remove Rev B because it just complicates things. “If Rev B, refer to FDC+ manual”.

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[Mike Douglas]

Note: The statement "All switch settings are read and latched only at power-on, so any changes require cycling power to the system" applies only to the drive type/monitor enable DIP switch S3. All other DIP switches (RAM, EPROM and interrupt configuration) are "real time" and changes are immediately in effect.

Mike D