UART (16550) multiplier simulation ?

[iamplouf]

Hello

i was trying to get higher baudrates than 115200 in DOS, and found that DOS has a hardcoded limit in 115200 .

Searching around found that cards existed to byapss this using multiplier
thats setting a internal multipleir in specific cards to 4x, then set dos regiseter to 115200, and the card actually clocked to 115200*4=460800baud .

is there any way to simulate this behaviour in DOSBOX ?
i.e. set a multiplier somewhere so when i config my DOS program to 115200 dosbox actually connect to 460800baud ?

thanx in advance

[joncampbell123]

Which cards allowed that?

As far as I know, standard UARTs, including the ones built into motherboards, divide down from 115200 and cannot go any higher, even if the UART offers a FIFO.

[iamplouf]

Thats what i found

But as i understand some high speed cards haad a multiplier
So i set multiplier x4 ,lets say multiplier is jumper in card itself.(Or a fossil driver like x00 as google says)

That way motherboard/bios config im 115200
But the card it self is higher

So is there a way to similate this in dosbox?
Thats, setting dos in 115200 but dosbox connect to 460800 in windows driver ?!

Thanx

[iamplouf]

ok i found thas dosbox-x has already a multiplier config in serialport
i set
realport:com3 multiplier:4

believeing that when a DOS program starts, which config port @ 9600, dosbox will actualyl clock realport to 9600*4=38400
however dosbox-x did the oposite i.e. it connect at 2400

do i do something wrong ?
using dosbox-x 2026-6-2 under windwos 11