RAM

From C64-Wiki

RAM is a shorcut for Random Access Memory. The Chips of computers, which are used as temporary memory, are called RAM. The input - also programs and datas - will be loaded into the ram before the CPU can be run this porgram. RAM-Chips can be also used as caches in harddisks, CD- or DVD-drives or as videoraum (VRAM).

The C64 has got a RAM of 64 KBytes (65536 Bytes). Useable are circa 39 KB for BASIC-programs. In the originally version are used 8 RAM-chips with 8 KByte. The chip-synonym is 4164. In the newer version C64C only used 2 RAM-chips with 32 KByte (chip-synonym 4464). The RAM of the C64 is so-called DRAM (shortcut for Dynamic RAM). The informations of a DRAM must be refreshed after a few seconds.

The chip-synonym of the Colour-RAM is 2114 with 0,5 KByte. The Colour-RAM used SRAM (shortcut for Static RAM). This RAM-type don't need a refresh.

The RAM of the C64 can be enhanced with cartridges. The famous Memory Cartridge is builded from Commodore and is called REU (RAM Expansion Unit). Another Memory cartrdige is called GeoRAM, which are only used with the operating system GEOS.

This article is under construction and classified as "work in progress" !!!

PS: Sorry the article at this line must be translated from German into English.

[edit] Pinouts of RAM chips in the C-64

2114 1K x 4 SRAM.
One of these makes up the text screen color RAM at 55296–56295/$D800–DBE7. Three of these chips (expandable by another 8) make up the main memory in the VIC-20.

    +---+--+---+
 A6 |1  +--+ 18| VCC
 A5 |2       17| A7
 A4 |3       16| A8
 A3 |4       15| A9
 A0 |5  2114 14| D1
 A1 |6       13| D2
 A2 |7       12| D3
/CS |8       11| D4
GND |9       10| /WE
    +----------+

4116 16 K x 1 DRAM.
Needs −5, +5 and +12 volt power supply.

    +---+--+---+
VEE |1  +--+ 16| GND
  D |2       15| CAS
 WE |3       14| Q
RAS |4  4116 13| A6
 A0 |5       12| A3
 A2 |6       11| A4
 A1 |7       10| A5
VDD |8        9| VCC
    +----------+

Here is a link to an article about using 4164 chips in place of the original 4116s: Bild

• Bend pin 1 und 8 upwards so they no longer go into the socket's connectors.
• Connect Pin 8 and 9 with one another through a short piece of wire.
• Make sure pin 1 and 8 are not in contact with any other components nearby.
• Insert the chip like this into the socket.

4164 64 K x 1 DRAM.

    +---+--+---+
    |1  +--+ 16| GND
  D |2       15| CAS
 WE |3       14| Q
RAS |4  4164 13| A6
 A0 |5       12| A3
 A2 |6       11| A4
 A1 |7       10| A5
VCC |8        9| A7
    +----------+

If you need one of the 4164 chips, you can also use a 41256 instead. You have to solder a short piece of wire between pins 1 and 16 of that chip (these are the pins just left and right of the alignment notch on the chip). This mod will make the chip look just like a '64 chip to the system.

4464 64 K x 4 DRAM.

    +---+--+---+
 OE |1  +--+ 18| GND
 D0 |2       17| D3
 D1 |3       16| CAS
 WE |4       15| D2
 RAS|5  4464 14| A0
 A6 |6       13| A1
 A5 |7       12| A2
 A4 |8       11| A3
VCC |9       10| A7
    +----------+

41256, 41257 256 K x 1 DRAM.

     +---+--+---+
  A8 |1  +--+ 16| GND
   D |2       15| CAS
  WE |3       14| Q
  RAS|4 41256 13| A6
  A0 |5 41257 12| A3
  A2 |6       11| A4
  A1 |7       10| A5
 VCC |8        9| A7
     +----------+

44256, 44258 256 K x 4 DRAM.

    +---+--+---+
 D0 |1  +--+ 20| GND
 D1 |2       19| D3
 WE |3       18| D2
 RAS|4       17| CAS
    |5 44256 16| OE
 A0 |6 44258 15| A8
 A1 |7       14| A7
 A2 |8       13| A6
 A3 |9       12| A5
VCC |10      11| A4
    +----------+

[edit] Cross-Referenz-Tabelle

Anhand der Cross-Referenz-Tabelle kann man die Typenbezeichnung der einzelnen Hersteller für die RAM-Chips ersehen. Obwohl elektrisch und mechanisch praktisch identisch, hat jeder Hersteller sein eigenes System, die entsprechenden Speicherchips zu kennzeichnen. Während die vorangestellten Buchstaben oft einen Hinweis auf den Hersteller geben, gibt die darauf folgende Ziffernfolge die Größe und Organisation des Speichers an. Darauf folgt oft ein oder mehrere Buchstaben, die meist die Gehäuseform bezeichnen. Schliesslich folgt dann wiederum eine oder mehrere Ziffern, zum Beispiel "-15", damit wird eine Aussage über die maximale Zugriffsgeschwindigkeit gemacht.

Beispiel: 2114L2 - dieser Speicherbaustein hat eine Zugriffszeit von 120 ns (Nanosekunden) und kann problemlos durch einen schnelleren Baustein 2114L1 (100ns) ersetzt werden, nicht jedoch durch einen 2114L3 (150ns) oder 2114L4 (200ns). Wie auch heute beim PC muss man also nicht nur die passende Speichergröße auswählen, sondern auch wissen, wo die Grenze für die Zugriffszeit liegt.

Speicherbausteine die in Commodore Computern eingebaut sind
Typ Hersteller	2114 1024 x 4 SRAM	4164 64K x 1 DRAM
Hitachi	HM 472114	HM 4864
Intel	P2114	?
OKI	?	M 3764 A
Mitsubishi	?
Motorola	?	MCM 6665 AP
NEC	uPD2114LC	?
Solid State Scientific	SCM2114AL
Toshiba	?

[edit] Links

Access Memory Wikipedia: Random Access Memory

Wikipedia: Speichererweiterung