Product: Mode 7 Mark 2 Display Unit
Publisher: Jafa Systems
Compatibility: Acorn Electron
Reviewed by: Derek Walker
Originally published in EUG #04

One More Mode

Jafa Systems has produced three Mode 7 products for the Electron. The first used the same integrated circuits as the BBC computer and the circuit board fitted between the Plus 1 and the Electron. It sold at £90 which was a bit expensive for the addition of one Mode. The adaptor was reviewed in the August 1987 edition of Electron User and in the May 1988 edition of Acorn User.

The second was an all-software solution where the program (held in ROM) simulates Mode 7 in Mode 2. This was much more affordable at £25 - but it had a few drawbacks. A review of this product was published in the May 1989 edition of Electron User.

The third, and most recent, is the Mode 7 Mk 2 unit, a combination of the Mode 7 board and the Mode 7 Simulator ROM. The display chip used in the BBC gives the teletext characters, but this time the ROM uses Mode 4 for memory scanning. The adaptor is compatible with the basic Electron and the two main memory expansions: Slogger's MRB and the E2P Second Processor (either from Permanent Memory Systems or Jafa themselves). HIMEM is &4000 (approx. 12k free memory for DFS, 8.5k for ADFS) for the unexpanded Electron while with the Master RAM Board, HIMEM is at &7C00 (approx. 28k free memory for DFS, 24k for ADFS). The adaptor can be purchased as a kit, built or built and installed. The kit comprises of a ROM, two circuit boards and instructions.

How It Fits

Once the components are soldered in place, the two circuit boards are connected using ribbon cable. The smaller board is soldered onto the ULA underneath the Electron's circuit board with the ribbon cable folded round resting the larger board on top of the ULA. The ULA sockets in some Electrons are quite tall and it can be a tight squeeze to get the lid back on. Also it restricts the air flow around the ULA therefore causing the Electron to run a bit warmer. I have had no problems with overheating in the couple of years since I installed the unit. There is no ROM socket provided so the ROM has to fit elsewhere in your system.

How It Works

To enable Mode 7, type *MODE7ON (or *M7.) and press BREAK. From now on Mode 7 is selected the same way as Modes 1 to 6. Scrolling is a bit slow with long listings and it can take a long time to get to the bottom. So a way to speed things up a bit has been provided. Pressing CTRL while the listing is scrolling, updates the bottom line on the screen at a faster rate and when released the whole screen is updated.

There are a number of new star commands (see table 1), two of which change the way the function keys operate, *EFN (Electron functions) and *BFN (BBC functions). When Mode 7 is active, the function keys default to BBC functions.

As the name implies, the function keys behave as that of the BBC computer allowing you to obtain the extra functions you get when pressing SHIFT, CTRL or SHIFT and CTRL. The *EFN command returns the keyboard to Electron Functions and keywords.

All teletext control codes are catered for with the manual covering the basics. The BBC handbook should be purchased if more detail is required. Also on the ROM is software to enable the Electron to become a Viewdata terminal (if used in conjunction with an RS423 adaptor and modem). This facility allows the user to link up to services such as Prestel and view data bulletin boards. I have no experience in this area so I can't comment on its performance.

Conclusion

The manual is short but covers the basics. There are sections included on the use of Wordwise and the ATS teletext adaptor. I recommend buying the BBC User Manual for advanced programming. The adaptor doesn't make the Electron 100% compatible with the BBC Micro as a lot of software written depends on the BBC hardware. I have tried a few Mode 7 games, eg Kingdom (from the BBC Welcome Tape), Mastermind, etc and ROMs e.g. Wordwise, View, Viewsheet, etc without any problems. It also brightens up a lot of game introductions. I have found it incompatible with Slogger's Click and Expansion 2.00's Sideways RAM Printer Buffer although it works with the MRB Shadow RAM 12k buffer.

More Mode, Less Speed!!

Mode 7 slows down the operation of the machine considerably but the MRB or Turbo Board goes a long way to compensate for this loss. I use this product extensively when using the spreadsheet and word processor. So much so, I would like to see it being activated from power up and deactivated manually if not required. At around £50 it isn't cheap but it's well worth every penny.

*MODE7ON then BREAK activates the adaptor
*MODE7OFF then BREAK de-activates the adaptor
*MODE7. then BREAK toggles between the above two states
*EFN function keys as Electron
*BFN function keys as BBC
*GREEN emulates a green screen monitor
*TV changes the vertical position of the Mode 7 display
*MCOMM Viewdata/Prestel Comms terminal software
*MED demonstration Mode 7 screen editor
*H.BARS colour bars
*H.MODE7 list of *commands

Derek Walker, EUG #4