HISPEC Project Glossary of Technical Terms

The purpose of this glossary is to allow an informed computer _user_ to understand the terminology used by the computer engineers and hardcore hobbyists involved in the HISPEC project. I would consider myself to be an informed user, so I've used my knowledge as a baseline. If there is anything you would like to see added, e-mail glossary@mhairi.demon.co.uk, and I'll find it out and add it to this file. Send any comments to the same address.

Thanks to: Andrew Toone, Suzanne Archibald

Revision History

21 September 98 All new entries for CPUs now simply refer the reader to the Guide. Added 680x0 figures to the MIPs table to ease comparisons for those familiar with Amiga, Atari or older Apple machines.

 

ADC channels: ADC stands for Analog to Digital Conversion. The number of channels is the number of seperate inputs that can be converted from an analog signal to a digital signal. For example, the ARM7500 has 4 ADC channels for joystick connections, so 4 (analogue?) joysticks could be attached.

Analogue Sound Port: This can theoretically be wired directly to a analogue sound device (e.g. a speaker or a microphone) without any other components in between.

ARM7500 & 7500FE: CPUs that have been suggested as possibilities for the project. See the Guide for more details.

AT-style PC Bus: This is a bus the same as (or very similar too) the ISA bus used by PCs (although now fallen from grace). The performance of such a bus is poor by modern standards (33?Mbyte/sec bandwidth).

Banks: Glueless chips often split the memory map into banks, where each bank will have the relevant CS pins available, or in the case of DRAM, RAS and CAS signals.

CAS Signal: See RAS Signal (qv)

Combined i/d Cache: A single cache that caches both instruction and data (i and d).

CS Pins: SRAM (Static RAM) and IO chips usually require a CS (Chip Select) signal to notify them that the data on the address and data buses is aimed for them.

DIP: Dual inline package - the conventional variety of IC package which is rectangular a with row of pins on each of the two longer sides.

Footpad: Basically a map of the PCB pin locations (or in SMD, the solder pad locations), and usually silkscreen information for aligning the device too.

FPGA: Field Programmable Grid Array. Basically when a conventional chip is made up the layout is like a city map, with all the buildings and roads performing their specified tasks. A PGA is more like a city that is all buildings and roads and when you decide on the layout you basically burn in those routes and not use the others (this is a gross oversimplification!) so you are creating a chip that can have a lot of 'wasted' space but performs like the 'real thing'. Gate propagation delay (qv) is a problem for FPGAs, making them considerably slower than an equivalent chip manufactured by conventional methods.

Gate: AND, OR, NOT etc.

Gate Propagation Delay: The gate propagation is the speed at which the signals travel via each gate created. In a commercial chip this isn't a problem seeing as you've created the layout to perform a specific task only, but in a PGA you may have to use several building blocks to achieve the same effect so this introduces a 'delay'. The shorter the time for the signal to cross the gates the closer it performs to the original.

Glue Logic: Hardware that uses basic logic circuits (eg. AND gates) to connect complex chips (eg. processors and memory) together. Few chips can just plug together (eg. if you plugged a load of memory chips into a processor, how would each chip know it was needed, and not one of the others?).

Glueless: A glueless CPU is one which effectively has the necessary glue logic already onboard. The pins of the chip can be wired directly to other components (e.g. memory chips) with little or no intervening circuitry. This makes a glueless CPU ideal for our purposes, since we don't have the resources to design and prototype complex glue logic.

IPC: Institute for Interconnecting and Packaging Electronic Circuits. They are the people that set down what is standard in terms of pin spacing on IC's, and footpad layout, etc.

MIPS: Millions of Instructions Per Second - a crude CPU benchmark. Comparisons between CPUs of different families using this method are notoriously unreliable, but in any case here are some approximate figures:

Motorola 68000 at 7MHz 0.9

Motorola 68020 at 14MHz 2.1

Motorola 68030 at 16MHz 3.5

Motorola 68060 at 50MHz 40

Z380 @ 25MHz 12

ARM7500 @ 33MHz 30

ARM7500FE @ 40MHz 36

PowerPC 403GCX @ 80MHz 99

486 @ 25MHz 20

Pentium @ 60 MHz 100

Further figures are given in the Guide in the section for each CPU.

Microcontroller: A microcontroller is a CPU with RAM and ROM, and possibly other components, on the same chip. The term is often misused to refer a CPU designed for embedded use. Also, in the world of DSP's, Microcontroller is often used to refer to a mode of operation that (more closely) mimics the behaviour of a standard microprocessor or microcontroller (in reference to how the CPU interfaces with other chips).

NEC VR4101 & 4111: CPUs that have been suggested as possibilities for the project. See the Guide for more details.

PGA: Pin Grid Array. A method of attaching a CPU to a PCB, where a socket is attached to the PCB and the CPU placed in the socket. Used by the Pentium series of CPUs (including the Pentium Pro but not the Pentium II). PowerPC 403 & 750: CPUs that have been suggested as possibilities for the project. See the Guide for more details.

PQFP Package: Plastic Quad Flat Package. This is a type of chip, being a plastic square (or rectangle) with pins on all sides. It's 'flat' because QFP devices are traditionally only 2-3 mm high, or so. This also should point to a specific IPC footpad for that device (assuming you know the number of pins), however, there are so many deviations from the IPC standards for QFP that you really need to check each individual device's databooks to make sure that its IPC or if not, that you can use the footpad provided by the manufacturer. Attaching a 240 PQFP (as used by the ARM7500) using only a soldering iron (as opposed to a reflow oven) is possible, but it's not easy and it's very tedious.

Prototyping: In hardware, the process of wiring bits together, often initially with miles of wire, to test a circuit. Later prototypes will use circuit boards which are expensive to produce in small numbers, but will have to be tested and changed until the circuit works.

RAS Signal: RAS (and CAS, qv) signals are sent to a DRAM chip to tell it that the data on the address and data buses are meant for it. A RAS indicates that that the address bus data is a Row address, and a CAS indicates that a column address is on the way.

Reflow Oven: Way to make a Printed Circuit Board (PCB). Rather than use a soldering iron to melt solder (metal) over chip pins to connect them to a circuit board (which would be very difficult to do as components become smaller and smaller), these days, chips are placed on a circuit board and solder is encouraged to flow around all of the connections, joining them together. Purchasing a reflow oven for the purposes of the project would be considered a ludicrous waste by some. It has been suggested that it may be possible to arrange to pay for someone else to solder PCBs for us, though.

Serial Sound Port: A port that can be connected to most current audio ADC and DAC chips, which use a serial protocol. The most common protocol is Philips' standard I"dS (I squared S). The ARM7500 has a serial sound port, but not apparently one that complies to the Philips standard. Playing sound through this port would work something like this:

Sample data in memory -> ARM7500 -> DAC chip -> audio output socket -> speaker.

Shift Register: A shift register is a bitwise manipulator. It shifts a bit pattern to the left or right.

Silkscreen: A process whereby a layer of painted is applied to an already etched PCB. Normally takes the form of component IDs and text in white paint on the upper (component) side of the PCB.

SMD: Surface Mount Devices. Rather than having its pins poked through a PCB and soldered on the other side, it has its pins soldered directly onto pads. Usually smaller in all dimensions than an equivalent DIP (qv). SMD is preferable to to conventional PCBs from a perspective of production cost. Increased reliability has also been cited as an advantage. However, devices containing SMD components are more difficult to produce and repair.

Stereo positions: A noise made by your computer can be made to sound as though it comes from different positions by playing it louder out of one speaker than the other. If you can just turn each speaker on or off, you get three stereo positions (left, right and center). If you can alter the relative volumes, you can get more.

Z80 & Z380: CPUs that have been suggested as possibilities for the project. See the Guide for more details.