Moxa DA-681-I-DP-LX [15/37] Non standard baudrates

DA-681 Series WinXP Embedded User’s Manual Software Configuration

Non-standard Baudrates

Moxa’s UART ASIC, supports most non-standard baudrates in the range 50 bps to 921.6 Kbps. In

fact, supported baudrates are much denser towards the lower values. For example, no baudrates are

supported between the integers 5320 and 5323, but 49 baudrates are supported between the

integers 387 and 388. Of course this is the way it should be, since serial devices that require using

non-standard baudrates generally use slower baudrates.

Before using a serial device that requires using a non-standard baudrate, you must first check that

the DA-681 supports a baudrate within the tolerance specified by the serial device manufacturer.

Use the following formula to calculate which baudrates are supported by the DA-681:

(A) Baudrate = 921600/(N+M/8) bps, for N = 1, 2, …, 18431, M = 0, 1, 2, …, 7

(B) Baudrate = 8 x 921600/K bps, for K = 8, 9, …, 147456

If you are a programmer and you need to write a driver for your serial device, then you may need

to use formula A. If you have a serial device that requires using a non-standard baudrate, then you

can use formula B to determine if the DA-681 supports a baudrate within the tolerance specified

by the serial device manufacturer.

Example

: Your serial device requires using a baudrate of 5340 bps and has a tolerance of 2 bps.

Can the DA-681 be used with this device?

Solution

: Set formula B to the desired baudrate and then solve for K.

8 x 912600/K = 5338 ==> K = 1367.703259…

This shows that the supported baudrate closest to 5340 comes from setting K=1367 or K=1368.

K=1368 ==> Baudrate1 = 5336.842105...

K=1367 ==> Baudrate2 = 5340.746159…

Since 5338 – Baudrate1 < 2, we can see that the DA-681 supports the serial device.

Note that we can use formula A to generate the so-called “standard” baudrates, which come from

setting M=0, and setting N equal to certain integers.

Standard Baudrates

Baudrate N M Baudrate N M

921600 1 0 4800 192 0

460800 2 0 2400 384 0

230400 4 0 1800 512 0

115200 8 0 1200 768 0

57600 16 0 600 1536 0

38400 24 0 300 3072 0

19200 48 0 150 6144 0

9600 96 0 75 12288 0

7200 128 0 50 18432 0

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