by Mark Gordon
I developed the hard disk interface in response to the urging of my teenage son. He bought an Adam computer several years ago when he decided that he wasn't satisfied using our PC computer for his purposes - it didn't have enough games for him. After using the Adam for a while, he concluded that the tape system wasn't fast enough for him and bought a floppy disk. It didn't take him long after that to realize that there were faster storage peripherals available for other computers - so why not for the Adam?
He had been briefly involved with AWAUG several years ago but didn't join because he didn't drive and I wasn't crazy about driving him. Finally, after a significant amount of coercing from him, I agreed to develop a hard disk drive add-on product for the Adam.
I began designing the hard disk interface for him this last spring. We didn't know about any other hard disk interfaces until just recently when we discovered that BJ (Big John Lingrel) was developing one. By that time, I had the wire wrap version up and running. When I found out about it, I felt that I had too much time and effort invested to abandon the project. So we decided to proceed. One of the things that Scott didn't like about the design I had developed was that it occupied the center expansion slot in the Adam. He had a parallel printer interface in that slot and didn't want to give it up. So I agreed to put a printer interface on the board so he wouldn't have to. He was also not enthralled with the underwhelming performance of his internal 300 baud Adam modem and asked for an RS-232 port to control an external modem. Okay, I said, I'll see if I can fit a serial port on the interface board also.
We had all of that up and running in wire-wrap form when we went to the AWAUG meeting that BJ attended. Not knowing how BJ would respond to a potential competitor, we decided not to mention the product to him. However, at that meeting we discovered that most of the Adam hackers were connecting both an RS-232 80 column terminal and an external modem to the Adam. Knowing of a dual UART chip, we decided that we would further expand the interface board to handle two RS-232 ports, a parallel printer port, and a hard disk interface.
About the same time, I discovered a source of hard disk controllers that also had a floppy disk controller port on them. It took a while but I finally got both the hard and floppy disk controller ports working. We can now attach IBM-style floppy disk drives (360K/720K) to the controller as well as two hard disk drives. So much for the history. Now let me try to satisfactorily answer the questions you asked:
1. Can memory expanders be used with the hard drive interface, since they also need to occupy expansion slot #2 to function?
I was not aware of the memory expander products when I designed the Powermate products. Obviously, if they need to occupy the center expansion slot at the same time the user wants to run the Powermate, we have a basic conflict - both can't occupy the same physical space simultaneously. The Powermate interface board can function in either the first or the second slot - all of the signals that it needs are available at either connector. However, since Scott did not want to give up his internal modem, we decided on the middle slot. I could redesign the board for the first slot (and will investigate the possibility), but I would need some significant amount of user feedback as to which slot is preferable. This would also delay delivery of the product about two months.
2a. Are we using a PC or PC-XT type of controller?
We are not using a PC-type controller. I considered it but did not want to attempt to write drivers for one. There was also no good place to mount it and I did not want to extend the bus by the several feet it would take to mount it in an external enclosure.
2b. Will the serial and parallel ports be compatible with existing Adam add-on products such that Adam software designed for those products will be useable with our board?
I assigned the Powermate ports so that they would not interfere with any existing Adam products. That way the Powermate could be added to whatever the owner had already. I provided drivers in the Powermate BIOS to handle communications with all of the ports on the board. I do plan, however, to make bit and address assignments known so that existing software can be patched to work. I also would consider developing specific drivers or patches for a few key programs that need to know how to drive the ports.
3. Are we using surplus boards or custom designed boards to achieve the low price?
The Powermate design consists of three circuit boards:
The interface board that plugs into the Adam (in expansion slot #2) was designed completely by me and contains the 2 serial ports, a parallel printer port, and a hard disk controller interface port. An interface converter board (which I also designed) is installed inside the external disk chassis and allows the Adam board to interface with the disk controller board, also installed inside the external chassis.
The interface converter board provides two benefits - it allows me to use a 25 pin ribbon cable to connect the external chassis to the Adam, and it allows the external chassis' power supply to send plus and minus 12 volts to the interface board inside the Adam to run the serial ports.
The disk controller board is a commercially manufactured product made by a large reputable hard disk controller manufacturer. It has the ability to control 2 hard disk drives and 2 IBM-style floppy disk drives. I buy the controller boards in quantity from a reputable perveyor of new and used computer parts. Some batches are made up of entirely new boards. Other batches consist of a mixture of new and used products while others are entirely used. However, no matter what the status of the boards are, they all come tested and guaranteed to work. I then add a new product warantee to the overall Powermate product such that the user need not worry about a malfunction in the first 90 days.
I have tried to price the Powermate products as aggressively
as I can so that it is not outside the reach of the serious Adam
computer buff. I make a modest profit on each sale and probably
cannot go any lower on price or I won't make anything at all.
The most important aspect of the product, I believe, is that
it is a complete turnkey system for about the same total price
that you would pay for the hard disk components. It also does
not require any modifications to the Adam computer to install
it. Bundle that with all of its functionality (two serial ports,
a parallel printer port, and a hard disk) and expandability (up
to 2 hard disk drives and 2 floppy disk drives) and I don't see
how you can beat its' bang per buck with anything else available.