R4 and R5 are 0K resistors. 0K resistors actually exist, and are typically used in place of short pieces of wire. The advantage of a 0K resistor over a short piece of wire is that they can be picked and placed and soldered using the same equipment that handles resistors, thus saving the need of having a separate machine for short wires.
That is how they are being used here, as you can see from the layout diagram. R5 is used to carry the RST signal over another line on the board, and R4 serves the same function for VCC.
First question: should these even be included on the schematic? They only exist to work around a construction limitation due to the use of a single layer PCB. If the circuit was built on a two layer PCB, or a breadboard, or wire wrapped, there would be no 0K resistors needed. I thought that schematics were supposed to just convey the topology of the circuit, leaving things related to the practical difficulties of construction to other documents (like the layout diagram).
Second question: on the schematic, why is R5 shown as connecting RST to RST, but R4 is shown as connecting VCC to itself? They are both being used to take a line across another line, so why aren't the both drawn the same way on the schematic?
A 0 ohm resistor typically is only used for places where a different-valued resistor could be substituted or used to exist, or to act as an optional jumper on different revisions of hardware. In those cases, the resistor is in the schematics.
A circuit designed from the start with a 0 ohm resistor that was just used for connecting two points across some board feature would never make it past review where I used to work. Such a situation may come up due to later design changes or board damage, in which case the board is modified by use of a "blue wire", which is an actual blue-insulated wire that makes a point-to-point connection on the surface of the board. Those are not in the schematic.
That said, I used to work on military electronics. Perhaps the consumer electronics world is different.
Great questions. As you point out, I'm using the 0K resistors as jumper wires. It's a one-sided board so the 0K resistors basically act as a second layer on the board.
Regarding your first question, I am not sure how to place a component only on the layout diagram. This would be ideal, because the 0K resistors really shouldn't be encoded in the schematic.
I agree with your second point -- it's just an inconsistency in my schematic!
R4 and R5 are 0K resistors. 0K resistors actually exist, and are typically used in place of short pieces of wire. The advantage of a 0K resistor over a short piece of wire is that they can be picked and placed and soldered using the same equipment that handles resistors, thus saving the need of having a separate machine for short wires.
That is how they are being used here, as you can see from the layout diagram. R5 is used to carry the RST signal over another line on the board, and R4 serves the same function for VCC.
First question: should these even be included on the schematic? They only exist to work around a construction limitation due to the use of a single layer PCB. If the circuit was built on a two layer PCB, or a breadboard, or wire wrapped, there would be no 0K resistors needed. I thought that schematics were supposed to just convey the topology of the circuit, leaving things related to the practical difficulties of construction to other documents (like the layout diagram).
Second question: on the schematic, why is R5 shown as connecting RST to RST, but R4 is shown as connecting VCC to itself? They are both being used to take a line across another line, so why aren't the both drawn the same way on the schematic?