does 8250 uart require to match modem baud

Question

I am studying modem i/o and am setting the uart through com1: and the base address x03f8 and am wondering if the uart connection to the modem must be equal? I am doing this in QB64.

Answer 1

If you're referring to the baud rate, then the com port setting must be the same or higher than the modem baud rate desired.

Answer 2

After opening the communications device as a file can you adjust the uart baud rate and set it to match the modem baud using the dlab register?

Answer 3

Found this DLAB subroutine:

' sets port dlab (Divisor Latch Access Bit)
SUB SetBPS (Var)
SELECT CASE Var
CASE 1 ' 19200
    LByte = 6
CASE 2 ' 38400
    LByte = 3
CASE 3 ' 57600
    LByte = 2
CASE 4 ' 115200
    LByte = 1
END SELECT
Var2 = Base.Address
IF Var2 = 0 THEN
    SELECT CASE Port
    CASE 0
        Var2 = &H3F8
    CASE 1
        Var2 = &H2F8
    CASE 2
        Var2 = &H3E8
    CASE 3
        Var2 = &H2E8
    CASE 4
        Var2 = &H3E0
    CASE 5
        Var2 = &H2E0
    CASE 6
        Var2 = &H338
    CASE 7
        Var2 = &H238
    CASE ELSE
        EXIT SUB
    END SELECT
END IF
' divisor latch low
LSB = Var2 ' 3F8x
' divisor latch high
MSB = Var2 + 1 ' 3F9x
' line control register
LCR = Var2 + 3 ' 3FBx
MSBSave = INP(MSB)
OUT MSB, 0
OUT LCR, 128 ' dlab
' set baud rate
OUT LSB, LByte ' least significant byte
OUT MSB, 0 ' most significant byte
OUT LCR, 3 ' n,8,1
OUT MSB, MSBSave
END SUB