Bally Astrocade

Nutting and Midway

In the late 1970s, Midway contracted Dave Nutting Associates to design a video display chip that could be used in all of their videogame systems, from standup arcade games, to a home computer system. The system Nutting delivered was used in most of Midway's classic arcade games of the era, including Gorf and Wizard of Wor. The chipset supported what was at that time relatively high resolution of 320×204 in four colours per line, although to access this mode required memory that could be accessed at a faster rate than the common 2 MHz dynamic RAM of the era.

Console use

Originally referred to as the Bally Home Library Computer, it was released in 1977 but available only through mail order. Delays in the production meant none of the units actually shipped until 1978, and by this time the machine had been renamed the Bally Professional Arcade. In this form it sold mostly at computer stores and had little retail exposure, unlike the widely available Atari VCS. In 1979, Bally grew less interested in the arcade market and decided to sell off their Consumer Products Division, including development and production of the game console.

At about the same time, a third-party group had been unsuccessfully attempting to bring their own console design to market as the Astrovision.^[2] A corporate buyer from Montgomery Ward who was in charge of the Bally system put the two groups in contact, and a deal was eventually arranged. In 1981, they re-released the unit with the BASIC cartridge included for free, this time known as the Bally Computer System, with the name changing again in 1982 to Astrocade. It sold under this name until the video game crash of 1983, and then disappeared around 1985.

Midway had long been planning to release an expansion system for the unit, known as the ZGRASS-100. The system was being developed by a group of computer artists at the University of Illinois at Chicago known as the 'Circle Graphics Habitat', along with programmers at Nutting. Midway felt that such a system, in an external box, would make the Astrocade more interesting to the market. However it was still not ready for release when Bally sold off the division. A small handful may have been produced as the ZGRASS-32 after the machine was re-released by Astrovision.

The ZGRASS system, combined into a single box, would eventually be released as the Datamax UV-1. Originally aimed at the home computer market while it was being designed, the UV-1 was re-targeted as a system for outputting high-quality graphics to videotape. These were offered for sale some time between 1980 and 1982, but it is unknown how many were built.

Language features

Astro BASIC supported the following keywords:^{[4]: 108-114}

• Commands: LIST, RUN, STOP, TRACE
• Statements: PRINT, INPUT
• Structure: GOTO, GOSUB, RETURN, IF (but no THEN and no ELSE), FOR-TO-STEP/NEXT
• Graphics: BOX, CLEAR, LINE
• Tape Commands: :PRINT, :INPUT, :LIST, :RUN
• Functions: ABS(), CALL(), JX() (specified joystick's horizontal position), JY() (joystick vertical position), KN() (knob status), PX(X,Y) (pixel on or off), RND(), TR() (trigger status)
• Built-in variables
  • (read only): KP (key press), RM (remainder of last division), SZ (memory size), XY (last LINE position)
  • (write only): SM= (scroll mode), TV= (display ASCII character)
  • (read/write): BC (background color), CX CY (cursor position), FC (foreground color), NT (note time),
• Math: + - × ÷
• Relational operators: < > = <= >= # [not equal] [the language did not support <>]
• Logical operators: × [AND] + [OR]

A period . at the start of the line was equivalent to REM in other BASIC implementations. Certain commands were handled by the keypad instead of by keywords: the RESET button was equivalent to NEW in other interpreters.

The language supported 26 integer variables A to Z, and two pre-defined arrays, @() - which was stored starting after the program, ascending - and *() - which was stored from the top of memory, descending. The language lacked a DIM statement for dimensioning the arrays, the size of which was determined by available memory (SZ) not used by the program listing (2 bytes per item). Ports were accessed via the array &(), and memory was accessed via the array %(), rather than using PEEK and POKE. While the language lacked strings, KP would provide the ASCII value of a key press, which could be output to TV, meaning that characters could be read in from the keyboard, stored in an array, and then output.

The character display was 11 lines of 26 characters across. The resolution for the graphic commands is 88x160, with X ranging from -80 to 79 and Y ranging from -44 to 43.

Music could be produced in four ways:^{[4]: 40,114}

1. The PRINT command, as a side effect, produced a unique tone for each character or keyword displayed.
2. The MU variable converted numbers into notes.
3. Ports 16 through 23 accessed a music synthesizer.
4. The sound-synthesizer variables MO (master oscillator), NM (Noise Mode), NV (Noise Volume), TA (Tone A), TB (Tone B), TC (Tone C), VA (Voice A volume), VB (Voice B volume), VC (Voice C volume), VF (Vibrato Frequency), VR (VibRato). (Added to Astro BASIC but not in Bally BASIC.)

Sample code

The following sample program from the manual demonstrates the joystick input and graphics functions. "Try your skill... The first player's knob moves the phaser left or right and the trigger shoots... Player two controls the target while player one shoots."^[4]: 72

  1 .PHASER PHUN
  2 .BY DICK AINSWORTH
 10 X=RND(60)-31
 20 Y=RND(20)
 30 CLEAR
 40 X=X+JX(2)×3
 50 Y=Y+JY(2)×3
 60 BOX X,Y,4,4,3
 70 K=KN(1)÷2
 80 BOX K,-40,3,8,1
 90 IF TR(1)=0GOTO 30
100 N=1
110 IF K>X-3IF K<X+3N=15
120 FOR A=1TO N
130 BOX K,0,1,80,3
140 MU="4"
150 BC=A×8
160 NEXT A
170 FC=7
180 BC=8
190 GOTO 10

This listing illustrates how keywords, which were tokenized, were always displayed with a following space.

Circuit board and cartridges

• CPU: Zilog Z80, 1.789 MHz
• RAM: 4 kB (up to 64 kB with external modules in the expansion port)
• ROM: 8 kB
• Cart ROM: 8 kB
• Expansion: 64 kB total
• Ports: 4 controller, 1 expansion, 1 light pen

Audio

• Sound chip model: 0066-117XX, also known as the Music Processor,^[8] or a custom I/O chip^[8][9] since the sound chip also performs I/O functions.
• Channel capabilities: There are 3 square wave channels, all with a pitch accuracy of 8-bits (256 possible frequencies from which to choose), which can all play square waves. The chip also has a noise generator, which can be independent from the other 3 square wave channels, or it can add its value to the master oscillator that drives the 3 square wave channels. The master oscillator can be set to different frequencies, which means that the frequency range can be changed for the 3 square wave channels.^[9]
• Volume control: Each channel has independent 4-bit volume control.^[9]
• Miscellaneous features concerning sound: There are hardware registers for vibrato, with two bits for the vibrato speed and 6 bits for vibrato depth.^[9] This means that it wouldn't be necessary for vibrato to be done entirely with software.

Video

• Resolution: True 160×102 / Basic 160×88 / Expanded RAM 320×204
• Colors: True 8* / Basic 2
  • The bitmap structure of the Bally actually only allows for 4 color settings. However, through the use of 2 color palettes and a left/right boundary control byte, the left section of screen (this could be the play field) could use one set of colors while the right side (this could show information such as lives and score) could use an entirely different set of colors, thus 8 total colors could possibly be displayed at once.
• Graphic type: Bitmap, 2 bit per pixel bit map.

Cartridges