Serial Ports: Difference between revisions
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The serial controller (UART) has an internal clock which runs at 115200 ticks per second and a clock divisor which is used to control the baud rate. This is exactly the same type of system used by the Programmable Interrupt Timer (PIT). |
The serial controller (UART) has an internal clock which runs at 115200 ticks per second and a clock divisor which is used to control the baud rate. This is exactly the same type of system used by the Programmable Interrupt Timer (PIT). |
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In order to set the speed of the port, calculate the divisor required for the given baud rate and program that in to the divisor register. For example, a divisor of 1 will give |
In order to set the speed of the port, calculate the divisor required for the given baud rate and program that in to the divisor register. For example, a divisor of 1 will give 115200 baud, a divisor of 2 will give 57600 baud, 3 will give 38400 baud, etc. |
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Do not be tempted to use a divisor of 0 to try to get an infinite baud rate, it won't work. Most serial controllers will generate a unspecified and unpredictable baud rate (and anyway infinite baud would mean infinite transmission errors as they are proportional.) |
Do not be tempted to use a divisor of 0 to try to get an infinite baud rate, it won't work. Most serial controllers will generate a unspecified and unpredictable baud rate (and anyway infinite baud would mean infinite transmission errors as they are proportional.) |
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