Aquarius Theory of Operation
| See also | ||
| POWER | Power is supplied to
the Aquarius by means of a cable mounted AC to DC power transformer. This
provides the computer with +8.8Vdc at 2.1A, +16Vdc 150mA, -19VDC 10mA Inside the Aquarius the regulator circuitry ensures stable supplies of +5Vdc, -5Vdc, +12Vdc and unregulated -12Vdc. |
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| CPU | The core of the system
is U1, the ZILOG Z80A Microprocessor,
which is a 8 bit processor running at 3.5Mhz. It has a 16 Bit address bus
and 8 Bit data bus. Some models had other manufactures of this chip,
mainly Sharp or NEC, but all are pin compatible. Upon power up the Z80 CPU sets all registers to 0x0000 and starts executing instructions from address 0x0000. The Aquarius does not make use of any Interrupts, which makes for easy programming, but means that when in BASIC mode the CPU must 'poll' the keyboard at frequent intervals to check if any keys are pressed. |
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| ROM | There are two ROM chips in the Aquarius. U2 which held the 8k BASIC Interpreter and U5 which holds all the character definitions. Only U2 is accessible by the CPU, U5 the Character Rom, is accessed by PLA2 which controls the video output. | |
| RAM | The Aquarius had only
4K of Ram, however 2.3K of this was taken up by Character and Colour
ram, system variables and stack space.
ROM : 0x0000 to 0x1fff |
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| Screen | The screen is laid out
as 25 rows of 40 columns, however BASIC never draws to column 0 or column
39, effectively limiting the display to 25x38 characters. There is no HI-RES mode, however the character set includes includes various symbols such as men, robots, geographical shapes and explosions, along with all the characters required to allow a psuedo 80x75 'graphics' mode. By poking values directly into the character or colour ram you could access the full 40x25 screen area. There is absolutely no support in the BASIC interpreter for changing the colour of text etc, but you could set any character position to any of the 16 foreground and/or back ground colours by poking the appropriate value into the colour ram. |
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| Keyboard | The Aquarius keyboard
was made from bright blue rubber keys with a sort of 'dead flesh' feel to
them, each a little less than 1 centimeter square, with the exception of
SHIFT, CTRL and RTN which were slightly bigger. Electronically the keyboard is set out in 8 columns of 6 rows, allowing for a total of 48 keys, plus CTRL and SHIFT. There is also a RESET key on the keyboard, and this is connected directly to the -RESET line of the processor, via a pull-up resistor. It was all to easy to hit the reset key by mistake, but fortunately the Aquarius ROM allowed you to hit CTRL+C on the start screen to recover from this without loosing your basic program. |
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| Sound | The basic Aquarius supports only 1 bit, mono sound, which was routed through the modulator into the TV set. You can specify the DURATION and PITCH in a basic SOUND statement but these values had no relation to real-life timings or frequencies. For example, a duration of 50 would last much longer for a low-frequency note than for a high-frequency note. You can directly control the speaker by writing 0 or 1 to bit 0 of port 0xfc | |
| Printer | The printer used a
cut-down version of an RS232 port, running at 1200 Baud. Although a 40 column printer was sold by Mattel for this machine, you could also use any SERIAL printer if you were handy with a soldering iron and can make the cable shown here. You can also connect the Aquarius to a PC using the same cable. |
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| Cassette | The sound port and the cassette port were actually one in the same. All sounds made by the Aquarius were also routed to the cassette port and all sounds sent to/from the cassette port were also relayed to the TV speaker. |