gordonl@microsoft.UUCP (Gordon LETWIN) (04/06/90)
re: the discussion of microcontrollers a while ago, my favorite is the Intel 8752. This is a member of the 8051 family, expanded to three timers, 256 bytes of ram and 8K of EPROM. The processor's architecture is not very elegant, but it's effective. It's an accumulator based machine for arithmetic operations but you can do memory operations out of a bank switchable set of registers. There are also immediate to memory operations, as well. There's a good set of bit manipulation instructions so that in a single, 1-microsecond instruction you can set, clear, compliment or test any of the I/O pins or any of a special set of 128 bits of the chip's RAM. Most instructions take 1 microsecond, some (like jumps) take two. I like the chip because it has 32 available I/O pins in a 40 pin package. The pins can be selected for input or output on a per-pin basis and changed at any time. 24 of the pins also have internal pullups. This large set of pins and the one-microsecond pin manipulation instructions make the chip a pretty effective general purpose engine. For example, if I want to drive some fancy UART, like the 82530, I just hook it's data pins to 8 of the 8752, hook the 5 or so control pins to 5 more 8752 pins, then write some simple software to wiggle the UARTs control pins in the proper patterns to make it talk to me. Likewise, I've hooked a couple of these together by just direct connecting some pins and writing a bidirection handshake/command interface. The main problem is that these puppies are about $100 each. That's an incredible price for a $4 CPU, but if you buy the CPU in it's $4 version you need external ROM/EPROM and accessing that external memory eats 16 of your 32 I/O pins. I recently noticed a Dallas Semiconductor DS500032-12 which is supposed to be a plug compatible 8751 chip. It has 32K of non-volitile RAM on board which the catalog blurb says can be used for "program or data". The RAM is preserved for a minimum of 10 years "in the absense of VCC". This sounds like it would be an ideal chip; it's cheaper (about $60) and it's got a lot more data space. (The chip architecture only directly addresses 256 bytes, but there are "read/write external RAM" instructions to access additional RAM) I've ordered an evaluation kit, but it's on indefinite back order. Is anyone familiar with this chip? I'd appreciate, via email or posting, a bit of info. I assume that it has the normal 128 bytes of RAM in addition to the 32K of additional RAM? Any problems or gotchas with this chip? thanks gordon letwin uunet!microsoft!gordonl uw-beaver!microsoft!gordonl