David A. Hook
An EPROM is an Erasable Programmable Read Only Memory. It is similar to the ROM chips inside the computer that hold BASIC, except that it can be erased, usually by exposing it to ultraviolet light for a period of time. It is useful if you have a program, such as Micromon (COMPUTE!, January, 1982, #20, pg. 160) which you use quite often. Instead of having to load it into the computer each time, it could be saved onto an EPROM, pushed into one of the empty sockets in your machine, and then used by a SYS to its starting location. This is sometimes called firmware, falling, as it does, between soft- and hardware.
The Branding Iron is a versatile EPROM burner for Pet 2001, CBM 4000 and 8000 series computers. The software provided functions with Original ROM, Upgrade ROM, or ROM 4.0 (both 40-column and 80-column).
Software and hardware allow programming of the three PET-compatible EPROMs: Intel 2716 or TI 2516 (both 2K) and TI 2532 (4K). The single, 5-volt, version is the correct type for the PET.
You may: program an EPROM, verify the contents of the EPROM just programmed, or copy an EPROM's contents into the PET's memory.
The Branding Iron consists of a 5"x 5"x 1" module and two connectors. One attaches to the User Port and the other to the 2nd Cassette Port. Ribbon cables are connected to the main unit. A 250 mA transformer provides the power and is to be plugged into a nearby AC socket.
The main module is attractively housed: no bare circuit board. Rubber feet should prevent scratches to your table. The 24-pin socket is not a "zero insertion-force" type. However, it has been gentle to the fragile IC-leads so far. There is a read/program switch and a status light to show programming activity.
The two cables are approximately 24 inches long. Both connectors are marked to show the "up" side. Neither included polarizing keys to prevent upside-down insertion. This 10-cent cost should not have been omitted. (The etched markings on my User Port connector were not painted).
Four typewritten pages of instructions are included. They indicate the location of the proper cassette port for each model PET/CBM. Most large keyboard, 40-column, machines make this connection inside the case. If your machine was upgraded from a built-in cassette, this port will be external.
I chose to plug in the transformer at a different wall socket than the PET.
The first program on the cassette provides several screens of instructions. The proper syntax and function for each command is shown.
You are then offered a choice of four programs, or a return to the start of the instructions. Then hit 'RETURN' and the tape will seek and load the chosen program. If you are working from disk, add ',8' to the 'LOAD' command on the screen.
The proper 'SYS' command has also been printed on the screen. Move the cursor here and hit 'RETURN'. The software has now been linked to the normal machine language monitor. Four extra commands are now available: T,P,V and C.
The documentation also gives the memory addresses used by each program. This is helpful — you won't accidentally use these yourself.
'T' Command: selects the type of EPROM. Defaults to a 2716 or 16K bit ('.T 16'). Enter '.T 32' for a 2532. No need to re-enter for each EPROM, unless you're switching types.
'P' Command: programs the EPROM from PET memory, given a start/end address in hexadecimal. Follow the manual directions for the 7-step procedure.
An address counter increments on the screen during programming. Any errors or defective memory locations are displayed on the PET's screen. Two minutes later it's done.
It isn't necessary to program the entire contents of the EPROM at any one session! This feature is quite significant. It is shown in the demo program, but not emphasized. Because of this, it is important to program from PET memory carefully.
If you want to store into the first byte of the EPROM, be sure to have this byte at a "round" hex address in the PET. (e.g. $2000, $3000, $4000, etc.).
Correspondingly, to program the fifth 256-byte "page" of the EPROM, you might enter: '.P 2400 24FF'. I have programmed as few as 21 bytes in a session.
'V' Command: compares the EPROM's contents with a given range of PET memory. It's done in an instant. Any discrepancies are reported, giving: memory address, PET memory contents, and EPROM contents at that address.
'C' Command: the EPROM contents are transferred to the user-designated range of PET memory. This too is almost instantaneous.
You may then examine or edit, using the normal PET monitor commands.
I've programmed both 2K and 4K EPROM's with this device. All features have worked flawlessly.
It's very versatile: all PET/CBM hardware, software for all PET ROMs and all compatible EPROMs. All this for a reasonable price.
With all the utilities now available for the PET, EPROMs to expand user-memory are a valuable enhancement. The PET's character-generator is another candidate for an EPROM.
Producer: K-Z Systems, Rt. 2, Box 473
Manchester, MO 63011
Availability: AB Computers, 115 E. Stump Road
Montgomeryville, PA 18936
Cost: $79, plus shipping