Discuss What is the best signal interface for PC ? in the UK Electrical Forum area at ElectriciansForums.net
BECAUSE I had to deal with limited (8pin Outputs) number on the memory IC, I had to be 'smart' about it.Please clarify for me how you intend your logic to scan the LEDs of the 7 x 5 matrix.
Slight correction inserted to text above.Now that you have clarified what I suspected may I suggest that you do not need to drive the 74138 by four data outputs of the RAM2732. Drive the 138 using the same 3 lines (1,2,4) of the 7493. This will still cause your display to be scanned line by line, top to bottom and then repeated. ie 7 lines
Now you have 8 data outputs. You can use the first 5 - D0 to D4 - of them to set the state of illumination state of each LED in a line. eg (00100) (010010) (10001) (10001) (11111) (10001) (10001) for the letter A
Now turn your attention to the address word which is 12 bits long A0 to A11. Use A0 to A2 (ie 1, 2 and 4) as now connected to the 7494 so that for any state of bits A3 to A11 the 7493 will cycle through 7 memory locations. These 7 memory locations are a unique group determined by bits A3 to A11. This means you can store in the RAM 2exp9 number of unique groups of 8 bit data outputs of which you will use 5 bits for a line of 5 LEDs.
One could write the Address word A as ( A11, A10, A9......................A2, A1, A0) = (Character Identifier Address (9bits) Character Font Code Addresses(3bits))
The 7493 will always cycle through A2,A1 and A0 to output the 7 five bit line patterns of a character font. You only need to select which character font you want to display by setting the Character Identifier Address A11 to A3.
Thus letter A could have the Character Identifier Address 000 000 001 A2, A1, A0
Letter B could have 000 000 010 A2, A1, A0
Letter C ......000 000 011 A2, A1, A0
Letter D........000 000 100 A2, A1, A0
Thus by setting the Character Identifier Address you can pick a character to display. Of course you have to programme the seven memory locations addressed by the Address Word A - character identifier address in red- so that they contain the appropriate bit patterns for the seven lines which make up a character.
This was truly very smart correction ! I didn't see it and I like it. I build it, tested and I confirm it works. Very logical !...may I suggest that you do not need to drive the 74138 by four data outputs of the RAM2732. Drive the 138 using the same 3 lines (1,2,4) of the 7493. ...
Ok, thank you. So it was a secondary 7493 IC linked to the same clock. Very ingenious from you mister @marconi. I will construct it.To construct an 8 bit counter to connect to A11 (msb) through to A3(lsb) on the 2732 cascade two 7493s together so that Qd of the first ic connects to clkAbar of the second. Remember to connect Qa to clkB bar on each chip.
Use the pulse circuit in # to produce a negative going pulse upon depression of the push button and connect it to clkAbar of the first ic.
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