Memory organization of the VG5000µ
Advertisement announces VG5000 has 24 KB RAM and 18 KB ROM.
Here are the inscriptions written on the VG5000
case:
ROM (Read Only Memory)
16 KB contains Basic and the BIOS of the VG5000, and the 2 additionnal
KB are reserved for the charset (2048 bytes held in the video processor EF9345).
There are 2 versions of the VG5000 ROM, one with Basic v1.0, held in two 8 KB
ROM circuits, and one with Basic 1.1, held in one 16 KB ROM circuit.
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2 circuits TMS4764 version |
The doughter board including the 2 ROMS |
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Here, the daughter board has been removed,
you can insert the 9128C ROM from GI |
left side, the 9128C
GI ROM |
You may notice, that the VG5000 with Basic 1.0 version was planned
with only one ROM circuit (16 KB TMS47128). But, because of a lack of supply,
the VG5000 will be temporarily equipped with two 8 KB ROM circuits (TMS4764).
A few hundreds of units where build with those 2 ROM circuits.
For the 1.1 version, Philips will use a GI 9128C ROM circuit.
GI 9128C ROM circuit datasheet - 16 KB
RAM (Random Access Memory)
VG5000 embeds 24 KB (3 x 8 KB) type SRAM
D4168C (200ns)
Memory distribution:
2 x 8 KB : used by the system
1 x 8 KB : used by the video processor
Internal view:
Finally, with a basic version, there are 13758 bytes free
available for your program.
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basic version with a Basic 1.0 rom |
basic version with a Basic 1.1 rom |
For the programmers, here is the memory map of the VG5000
SRAM D4168C (200ns) Datasheet
VG5216 extension
With the VG5216, 16 KB de RAM are added to the system
(as long as joystick, printer and bus extensions). There are 30142 bytes
available.
The inscriptions on the VG5216 case:
Internal view:
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basic version with VG5216 extension |
basic version with VG5216 andLgraph* |
* Lgraph is a software (Basic) extension to add
bitmap capability to printing. |
VU0031 cartridge
The VU0031 adds 2 x 8 KB type SRAM D41416C (150ns). There
are 46526 bytes available.
The inscriptions on the VU0031 case:
Internal view:
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basic version + VG5216 + VU0031 |
basic version + VG5216 + VU0031 + Lgraph* |
* Lgraph is a software (Basic) extension to add
bitmap capability to printing. |
Summary:
Configuration |
commercial total |
Real |
Available (for the Basic) |
VG5000 |
24 KB |
16 KB |
13758 bytes |
VG5000 + VG5216 |
40 KB |
32 KB |
30142 bytes |
VG5000 + VG5216 + VU0031 |
56 KB |
48 KB |
46526 bytes |
In Basic : PRINT
FRE(0) prints the user memory available.
And now ?
To be done:
SRAM D41416C (150ns) [VG5216] Datasheet
Trick:
Where can you find spare RAM circuits? Answer: in a Sega Master System, it uses
the same SRAM circuits.
Project:
Upgrade the VG5216 with 2 16 KB RAM circuits to free the cartridge port...
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