Wiring skills: Serial direct connection cable connection (1)

The serial direct connection uses the COM port of the computer. Each computer has at least two COM ports, COM1 and COM2. "COM" indicates "communication ". Compared with the parallel port, its pins are much simpler, but the speed is also slower.

How fast (or slow) is the serial port speed? The fastest speed is about 12 to 14KB per second. This is quite slow for network connections. Let's take a look at how serial data is transmitted so that you can understand why it is so slow:

Shows how serial data is transmitted. The color block of each serial number is sent from PC1 to pc2. PC2 receives data in the transmission order. In other words, it receives data block 1 first and then 2 until data block 7. This is a representative data stream in the serial cable. The serial port transmits data sequentially over a pair of cables (other wires are used to control transmission ).

Another way is to use it as a one-way street with only one vehicle at a time (in our example above, there is only one data block at a time ), therefore, you can imagine that this street cannot handle several vehicles at the same time.

Serial Port

Many new computers have two 9-pin COM ports; this is the DB-9 positive connector. Vintage computer has a DB-9 positive connector and a DB-25 positive connector. The 25 positive connector is similar to the 9 pin, but it is relatively large.

Let's see what the serial port is like:

DB-9 and DB-25 use different pin distributions, so let's look at it later. Let's take a quick look at the COM port of the new computer:

Note that both COM ports have DB-9 connectors, but no DB-25. The two blue COM ports in the connector are LPT or parallel ports.

The serial port of the computer can run at different speeds, so that we can connect to different devices that communicate with the computer at different speeds. The following table shows the speed at which the serial ports of most computers run and how many KB/s they transmit:

Now let's take a look at pin distribution in DB-9 and DB-25 connectors: