Controlling Multiport Serial I/O Cards

The Microsoft serial driver can be used to control many dumb multiport serial cards. Dumb indicates that the control includes no onboard processor. Each port of a multiport board has a separate subkey under the CurrentControlSet\Services\Serial subkey in the Registry. In each of these subkeys, you must add values for DosDevices, Interrupt, InterruptStatus, PortAddress, and PortIndex, because these are not detected by the Hardware Detector. (For descriptions and ranges for these values, see "Disk, Serial, and Parallel Port Entries" in Chapter 14, "Registry Value Entries.")

For example, if you have a four-port COMTROL Hostess 550 board configured to use address 0x500 with an interrupt of 0x2, the values in the Registry would be as follows:

Serial2 subkey:

PortAddress = REG_DWORD 0x500
Interrupt = REG_DWORD 2
DosDevices = REG_SZ COM3
InterruptStatus = REG_DWORD 0x507
PortIndex = REG_DWORD 1

Serial3 subkey:

PortAddress = REG_DWORD 0x508
Interrupt = REG_DWORD 2
DosDevices = REG_SZ COM4
InterruptStatus = REG_DWORD 0x507
PortIndex = REG_DWORD 2

Serial4 subkey:

PortAddress = REG_DWORD 0x510
Interrupt = REG_DWORD 2
DosDevices = REG_SZ COM5
InterruptStatus = REG_DWORD 0x507
PortIndex = REG_DWORD 3

Serial5 subkey:

PortAddress = REG_DWORD 0x518
Interrupt = REG_DWORD 2
DosDevices = REG_SZ COM6
InterruptStatus = REG_DWORD 0x507
PortIndex = REG_DWORD 4

Certain multiport boards, such as Digiboard non-MCA bus cards, use a different scheme to determine which port is interrupting. These boards should include the Indexed value entry in the configuration data for each port under its subkey in CurrentControlSet\Services\Serial. This entry indicates that the board uses an indexed interrupt notification scheme as opposed to a bitmapped method.

For example, if you have an eight-port Digiboard communications board configured to be at address 0x100 with an interrupt of 0x3, the values in the Registry would be as follows:

Serial2 subkey:

PortAddress = REG_DWORD 0x100
Interrupt = REG_DWORD 3
DosDevices = REG_SZ COM3
InterruptStatus = REG_DWORD 0x140
Indexed = REG_DWORD 1
PortIndex = REG_DWORD 1

Serial3 subkey:

PortAddress = REG_DWORD 0x108
Interrupt = REG_DWORD 3
DosDevices = REG_SZ COM4
InterruptStatus = REG_DWORD 0x140
Indexed = REG_DWORD 1
PortIndex = REG_DWORD 2

Serial4 subkey:

PortAddress = REG_DWORD 0x110
Interrupt = REG_DWORD 3
DosDevices = REG_SZ COM5
InterruptStatus = REG_DWORD 0x140
Indexed = REG_DWORD 1
PortIndex = REG_DWORD 3

Serial5 subkey:

PortAddress = REG_DWORD 0x118
Interrupt = REG_DWORD 3
DosDevices = REG_SZ COM6
InterruptStatus = REG_DWORD 0x140
Indexed = REG_DWORD 1
PortIndex = REG_DWORD 4

Serial6 subkey:

PortAddress = REG_DWORD 0x120
Interrupt = REG_DWORD 3
DosDevices = REG_SZ COM7
InterruptStatus = REG_DWORD 0x140
Indexed = REG_DWORD 1
PortIndex = REG_DWORD 5

Serial7 subkey:

PortAddress = REG_DWORD 0x128
Interrupt = REG_DWORD 3
DosDevices = REG_SZ COM8
InterruptStatus = REG_DWORD 0x140
Indexed = REG_DWORD 1
PortIndex = REG_DWORD 6

Serial8 subkey:

PortAddress = REG_DWORD 0x130
Interrupt = REG_DWORD 3
DosDevices = REG_SZ COM9
InterruptStatus = REG_DWORD 0x140
Indexed = REG_DWORD 1
PortIndex = REG_DWORD 7

Serial9 subkey:

PortAddress = REG_DWORD 0x138
Interrupt = REG_DWORD 3
DosDevices = REG_SZ COM10
InterruptStatus = REG_DWORD 0x140
Indexed = REG_DWORD 1
PortIndex = REG_DWORD 8