Call for final Elf99 design input

Using as much Harris stuff as possible is not one of my design goals. Simplicity is. At the moment, the only Harris part may be the 1802 mostly due to cost. The Harris stuff is between $5 and $10 per chip. That was the gist of my questions. It appears that we were using terms that the other was not fully understanding. The term "memory space" that I used, refers to a region of memory that is designed to contain something, but may or may not be full. For example, a 4K PET has 32K of RAM address space, but 4K of RAM. It's trivial to add another 28K of RAM, not so trivial to add RAM outside of that 32K address space. A 68000 smart serial card I used to make had the 16Mb divided into 4 address spaces: RAM, I/O, shared memory (it was a DMA card on a PDP-11) and ROM. Even though no card ever had more than 2Mb of RAM (the oldest card had 32K of 2114!), all of the later cards had 4Mb of the memory map blocked out for RAM. It is easy to divide the memory space into 1/2 RAM and 1/2 ROM. It's harder to divide it into 3/4 RAM and 1/4 ROM. It's even harder to divide it into 3/4 RAM, 1/8 ROM and 1/8 memory-mapped I/O, and it's hardest of all to make the division user configurable. A 48K Elf might be cool, but none of the ancient software knows much more than about 4K, leaving plenty of the intended 32K left for new stuff. Besides, I want to stick with one RAM chip and one ROM chip, for simplicity. No... the entire ROM maps at $0000 and $8000 until the first time that A15 gets set, then the flip-flip clears and RAM banks in at $0000 and ROM remains at $8000. This is easy to implement and fairly clean. No I/O address needs to be hung up as in the VIP design (62). Technolgically speaking, it's trivial. The issue is real estate. If I have to make the board bigger, the cost goes up. I'm thinking about designing and releasing a design for a piggyback board to plug into the 6116/62256 socket to adapt a pair of 1822/2101's. I wouldn't *make* that board, but anyone who wanted to use 256x4 RAMs should be able to make their own. Now... OTOH, Allison Parent's mentioning of the COSMAC eval kit has pushed me back to considering dual 1852's. It's still the most expensive option, but software compatibility for any sort of existing software base is nothing to be lightly dismissed. If I understand what you are suggestion, Allison suggested that, too. You mean decoding additional secondary ports from a primary port, yes? The reasons not to do it are a) increased complexity of design and b) increased complexity of programming. I have not utterly dismissed it, but neither am I overwhelmingly convinced that it's necessary. They cost more. I can get 4/8-bit PIO displays 16x1 for $3 each. I have an ASCII LCD - PIC-an-LCD from B.G. Micro. The board was $12, the PIC controller was $12. I like it a lot. It sits on my Linux Internet router. Sticking with an easy to implement LCD connector means that the user can hang a *cheap* display right off the Elf. Ack! Too complicated. I'm after *simple* here. While your concept here is very powerful, It is and it isn't, depending on the nature of the playing. After all, you can't stick a logic probe inside a 185x chip. You *can* watch a 4308 latch the data and observe how a parallel port works, if you care to. Besides, the 1852 is nearly 10 times the cost of the 4308. Yes, but even a real RCA product, the VIP, used 4308 latches for PIO. Well.. Duh. I meant, why go the trouble of a bank of hardware integer multiply units with no practical use in mind beforehand. For example, if I were building a PIC project board, I'd contemplate ways to attach a thermistor to play with computerized thermometer projects. I am at a loss to suggest to the user what they could do with a bank of 1855's to justify 1/6th of the space on the board. But the Intel architecture isn't sexy like the 1802. You can't build a ROMless 8018x system with 256 bytes of RAM. As complex as the Elf99 is turning out, I know it can be partially populated to produce a very good approximation of the original Quest design (leave off the address latch and all I/O except the Q LED). Someone wishing to build the whole design can stuff every crevice with parts and have an Elf beyond our wildest dreams of 1977. Optional isn't the issue. The cost of the board space is. I've already planned on lots of optional stuff (PIO, UART, more than 256 bytes of RAM). I'm not opposed to optional things. I am just trying to give as much expansion as $99 will allow. If the board costs more, it loses its audience. Too complicated for a $99 design. If by controller you mean a Hitachi 48440 or similar chip that sits between the raw LCD and provides the user with a font and parallel (4 or 8 bit) interface, then yes. $2 to $9 is a typical range, depending on new or used or backlight or not. I've got a 20x4 on my Linux box (as I said). I chose to spend $24 extra (I scrounged the power supply and box) to keep the programming from a UNIX machine simple. There is no such requirement on a toy board. No argument about the library boot. I spent lots of time entering in games from the VIP manual (I still have the tape!) So far we are in agreement. I don't expect anyone to buy this and build it into an Internet Coke machine or anything. In the abstract, I agree, but I still see no practical use for the MDU except as an expensive, flashy toy that would only appeal to a few people (less than 5%). I'm shooting for 80% or 90% audience acceptance for a feature. So far, that's 8 bits in, 8 bits out and some sort of serial port (plus the required switches, displays and Q). They would be a good audience. I got my hands on a Quest Elf when I was 11. It nand the PET profoundly affected my life and career path. -ethan