I have seen typical bus resistance as few ohms. For example on MAChX02 1200 ZE board the bus that connects FTDI chip and the FPGA has only around 11 Ohm resistance.
Is there any specific reason for keeping bus resistance small?
Thanks in advance
The reason that Bus resistance is normally small
bus
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It's one that doesn't share grounds between the two systems it is connecting. It does so by using either optical or magnetic links instead of voltage levels to transfer data.
simulate this circuit – Schematic created using CircuitLab
You can daisy-chain '595s as much as you want: simply connect the output of one to the input of the next one and connect their control signals together.
First shift the data for the SN76489 followed by the data for the AY-3-8912. Your code would hardly have to change; just shift 16 bits instead of 8.
Best Answer
Unless designed otherwise, logic drivers aren't very strong. The process of transmitting a signal can be modelled as charging a small capacitor (a few pf) on the device to be driven, through the resistance of the bus. The higher the resistance, the slower the rise time on the target.
For slow signals you can go up to a few hundred ohms, or insert 100 ohm resistors in a bus if you fear it may be accidentally driven from both ends.
11 ohms seems quite high for a PCB trace.