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|TTL-series 74219 SRAM demonstration
This applet demonstrates the
TTl-series 74219 16x4 bit SRAM circuit.
The memory matrix consists of 64 latches organized as 16 (2^4) words
of 4 bits each, accessible via separate input and output lines.
A 4 bit address input selects one of the 16 memory words.
TTL family of integrated circuits also contains two other 16x4 bit RAM chips
that are very similar to the 74219, namely, the 7489 and 74189 circuits.
For some obscure implementation reason, both the 7489 and 74189
integrated circuits use inverted outputs - the values on the
output bus are the inverse of the data previously written into the RAM.
See the 74189 applet for a live demonstration.
Use the property editor (popup menu->edit) to open the user interface
with the memory editor. It shows a table with the current memory data
contents (hex encoded), with the memory addresses on the left and
the data stored at the address on the right.
Additionally, the memory word last read and written are highlighted
in green and cyan colors (unless you use a personalized color scheme).
To edit the RAM contents, move the mouse to the memory cell in question,
click the left button, and then enter the new value as a hexadecimal
number via the keyboard. The 74219 RAM only stores 4-bit per memory word,
so that a single keystroke ('0' .. '9', 'a' .. 'f') is sufficient.
The behaviour of the 74219 circuit is controlled by just two active-low
control lines, namely the nCE (chip enable)
and nWE (write enable)
|Print version | Run this demo in the Hades editor (via Java WebStart)|
|Usage | FAQ | About | License | Feedback | Tutorial (PDF) | Referenzkarte (PDF, in German)|