RTL Logic

It is difficult to mix RTL and TTL in the same circuit, the supply voltage and logic levels are different. RTL chips are slower, and have different switching characteristics to TTL. If the devices are used as plain digital devices, and if the timing delays are not critical, then you should be able to built one of those circuits using entirley TTL devices. But if they use gates as oscillators or monostables (read : If there are RC networks about), then you will almost certainly need to make some changes. The other thing to watch out for is that many older logic families (certainly DTL, I suspect RTL too) had passive (resistive) pull-ups on the outputs, and could be wire-ANDed without problems. TTL, of course cannot, unless you use open-collector devices with an external pull-up resistor. The bottom line : You can almost certainly make a functionally-identical device with TTL and the changes will not be that major, but there could well be changes, It may not be just a matter of replacing a NAND gate with a NAND gate, etc. -tony