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notes on serial devices

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Thomas Bishop 2025-12-15 18:29:19 +00:00
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16
zk/Bus.md
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@ -4,8 +4,6 @@ tags:
- computer-architecture - computer-architecture
--- ---
# Bus
A bus is a communication system that transfers data between components inside a A bus is a communication system that transfers data between components inside a
computer, or between computers. computer, or between computers.
@ -35,19 +33,11 @@ can mean:
There is a distinction between buses that use **serial** and buses that use There is a distinction between buses that use **serial** and buses that use
**parallel transmission**. They are distinguished by the way in which the bits **parallel transmission**. They are distinguished by the way in which the bits
are transferred from one point to another, along the bus. are transferred from one point to another, along the bus. See
[Serial transmission](./Serial_transmission.md)
Serial Transmission is the type of transmission in which a single communication
link is used to transfer the data from an end to another. On other hand Parallel
Transmission is the transmission in which multiple parallel links are used that
transmit each bit of data simultaneously.
![Serial transmission](../img/serial-transmission.jpg)
![Parallel transmission](../img/parallel-transmission.jpg)
- Serial buses are cheaper to implement than parallel buses - Serial buses are cheaper to implement than parallel buses
- Serial buses operate at greater [latency](Bus.md#latency) than parallel buses - Serial buses operate at greater latency than parallel buses
## Latency ## Latency

8
zk/mosquitto_mqtt_client.md
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@ -65,3 +65,11 @@ This registers on the broker device:
Client (null) received PUBLISH (d0, q0, r0, m0, 'test_topic', ... (11 bytes)) Client (null) received PUBLISH (d0, q0, r0, m0, 'test_topic', ... (11 bytes))
hello world hello world
``` ```
## Topics are inherently ephemeral
Once you exit from `mosquitto_sub` the topic ceases to exist. You can't then
relisten to the topic later as it hasn't persisted.
Topics are ephemeral routing labels, not persistent database entities. Think of
them more like radio frequencies. They only exist whilst they are transmitting.