Memory Expanders For The VIC-20
Ottis Cowper, Technical Editor
Creative users have developed programs of surprising sophistication for the unexpanded VIC. However, some programmers have felt that working within the 3583 bytes left after BASIC grabs its share of the 5K of built-in memory puts unacceptable constraints on their creativity. As a result, memory expanders for the VIC began to appear very soon after the computer itself hit the shelves.
The simplest form of memory expansion is the RAM cartridge, which plugs into the memory expansion port on the back of the VIC. They usually expand memory in multiples of 8K, although the first VIC memory cartridges added only 3K. Some of these are still in circulation. The great advantage of the cartridges is their simplicity — just plug them in. The main disadvantage is a certain lack of flexibility: It is necessary to remove the memory cartridge to plug anything else into the expansion port — a game cartridge or the Super Expander, for example. This can be overcome by using a motherboard, a device which plugs into the memory expansion port and acts like a multioutlet extension cord for the port, and there are as many different motherboards available as there are RAM expansion cartridges. A second disadvantage is that it is not as easy to change the address range of the added memory when using cartridges as it is with some of the more complex expansion systems. This, however, really should not present a problem for most users.
Commodore RAM Cartridges
Commodore makes two expansion cartridges for the VIC: the VIC-1110, which provides 8K expansion, and the VIC-1111, which provides 16K expansion. An added feature of the 8K cartridge is that it can be set to one of four address ranges, and, if you have a motherboard, can be used in conjunction with the 16K cartridge to provide 24K expansion, the maximum amount VIC BASIC can use without special programming.
RAMAX By Apropos
RAMAX, made by Apropos Technology of Camarillo, California, is something of a fusion of a RAM cartridge to a motherboard. It provides 27K of expansion RAM and two additional cartridge slots. A DIP switch allows you to selectively activate 24K of the additional RAM in three 8K blocks. The additional 3K block, if activated, goes to fill a hole in the unexpanded VIC's RAM space between locations 1024 – 4095 where no built-in memory is installed. This is the same 3K block filled by the additional RAM in the Super Expander cartridge, and by the 3K plug-in cartridges. The 3K block can be added alone or in conjunction with any of the other 8K blocks. However, BASIC cannot use the 3K block along with the 8K blocks without special programming. With the 8K blocks activated, the 3K block can be used to hold redefined characters and machine language subroutines.
Various memory expanders are available for the VIC.
If a block of memory containing data is switched out, the data is still maintained until the computer is turned off. If the memory block is switched back in, the data can be accessed as before.
The two expansion slots can be used for game cartridges or for utility packages like VICMON or the Super Expander. However, the slots are not switched, so you must avoid inserting two cartridges which use the same address at the same time. There is a DIP switch on the RAMAX which disables memory in the range 40960 – 49151, the area used by most cartridge game ROMs. This provides a way to effectively switch on and off a game cartridge plugged into one of the slots.
There is one additional DIP switch on the RAMAX which provides a valuable feature: the warm start reset switch. If you've ever experienced a "lock up" resulting from a bug in a machine language program, you've probably wished for something that would allow you to regain control of your computer without having to turn it off. That's what the reset switch does.
The RAMAX draws its power from the VIC, but adds a 0.5 amp fuse to protect the computer from any short circuits on the board. This proved to be a valuable safety feature. On several occasions programmers here at COMPUTE! failed to heed Apropos' warning that cartridges should not be installed or removed from the RAMAX while the power was turned on. This resulted in blown fuses on the RAMAX. And without the fuse the VIC itself might have been damaged.
The RAMAX comes with a ten-day money-back guarantee and a six-month warranty on parts and labor. An extended service contract is also available. We were most impressed with Apropos' customer service. Shortly after we received our first RAMAX, Apropos detected a possible defect in the RAMAX and recalled for modification all boards that had been shipped. We had our new RAMAX back in a matter of days.
The RAMAX also comes with a very complete brochure explaining all the available memory configuration options.
Golden RAM By Voice World
The Golden RAM Expansion Chassis madé by Voice World of Del Mar, California, offers exceptional flexibility in configuring the expansion memory. The Golden RAM has 24K of memory in three 8K blocks. Each block can be installed at one of two starting addresses. One of the blocks can be switched to start at location 40960 ($A000), which is a special block in the VIC. Programs starting there, and beginning with the proper character sequence, will run automatically after a system reset. This is how cartridge games are made to start when the computer is turned on. As with the RAMAX, data is not lost when the blocks are switched in and out. Also, two of the 8K blocks of RAM can be switched to a read only mode in which they emulate ROM and cannot be overwritten (although all data is still lost when the power is turned off). These special features could be very valuable to those involved in serious program development, although the casual user may never find a need for all of them.
The Golden RAM includes four cartridge expansion slots. An excellent feature of this expander is that the four slots can be switched in and out. It is possible, for example, to leave your four favorite game cartridges plugged into your VIC at all times and simply switch in the one you wish to play. This ends the need to constantly plug and unplug cartridges. The Golden RAM also has a reset switch, a large push button which is a significant improvement over the tiny DIP switch for reset on the RAMAX.
As with the RAMAX, the Golden RAM draws its power from the VIC. It is equipped with a 0.5 amp fuse to protect the VIC from short circuits. A spare fuse is also supplied.
The Golden RAM comes with a full one-year warranty.
VIC-1110 8K RAM Cartridge
VIC-1111 16K RAM Cartridge
Commodore Business Machines
1200 Wilson Drive
West Chester, PA 19380
$49.95 for 8K
$79.95 for 16K
1071-A Avenida Acaso
Camarillo, CA 93010
Golden RAM Expansion Chassis
13055 Via Esperia
Del Mar, CA 92014