Open-drain / open-source schematic for serial networking

doug.taylor

I want to network multiple BS2 stamps using the example in SEROUT (page 305) of BASIC Stamp Programming Manual Version 2.0b.· Specifically, the open-source circuit.· I am a programmer so the schematics make me nervous.

Looking at figure 5.37, there is a 1kOhm resistor between the I/O bus and ground.· But all other figures, such as figure 5.35 show a 10kOhm resistor between the flow control bus and ground.

Is the method in figure 5.37 completely different than the previous methods?· Is the ground in this figure merely a connection between VSS or is there a Pin involved such as in figure 5.35?

Most of all, I don’t want to chance shorting my BS2s.

doug.taylor

I had an epiphany.· Figure 5.37 represents the SEROUT circuit without the optional Fpin.



This leaves me without the benefits of flow control.· My question is now this:· Can I add an Fpin to the circuit in figure 5.37 to get the flow control, or is that only available in the two processor (speaker and listener) configuration?

Please see the attachment for pictures

allanlane5

Well, this does leave an open question. You want to 'bus' multiple BS2's together, right? But 'flow control' is the recieving BS2 telling the 'sending' BS2 when it is ready to recieve.

Now, in a 'bus' configuration, what does that signal mean? That all of the 'slave' BS2's are ready to recieve? That only one of them is?

I believe, typically in a 'bus' situation, you have the 'master' BS2 'ping' the 'slave' BS2's, and in the 'ping' have a byte which tells which of the 'slave' BS2's to 'answer'. If two 'slave' BS2's try to talk at the same time, the Open Collector bus won't be damaged, but the data will be garbled.

Oh, and if you put a 120 ohm resistor in series between each BS2 and the 'bus', even if everything goes wrong you shouldn't burn out a pin.

doug.taylor

Thanks for the reply allanlane5. I suspected something like this, but it is good to hear it from someone with a hardware background.

doug.taylor

allanlane5,

Is this what you meant with the 120 Ohm resistors?

allanlane5

Yup, that's what I meant.