6.4 MSI Board Functional Description

The MSI baseboard and each daughterboard contain eight line interfaces and eight COder/DECoders (CODECs). Each line interface provides loop-start current to one 2500 series equivalent station device.

The line interface also separates the inbound signal into an audio signal which is sent to the CODEC, and an on-hook/off-hook signal which is forwarded by the control processor to the application program.

The CODEC converts inbound audio to 8-bit PCM data and outbound PCM data to analog audio. The gain may be individually set for each station device.

A cross-point switch on the MSI board routes PCM data between the station devices, the DSP, and the SCbus.

The MSI board conferencing feature allows conferences to be established between SCbus time slots and/or station interfaces.

The control microprocessor executes commands received from the host PC, and controls all operations of the MSI board. Communications between the control microprocessor and the host PC is accomplished via a shared RAM interface mechanism.

Operations demanding real time responses are interrupt driven. All MSI boards installed in the PC share the same interrupt line. When the system is initialized, the firmware needed to control all board operations is downloaded from the host PC to the on-board RAM. The downloadable firmware enables easy feature enhancements in the future.

The Board Locator Technology (BLT) circuit operates in conjunction with a rotary switch to determine and set non-conflicting slot and IRQ interrupt-level parameters. This feature eliminates the need to set jumpers or DIP switches.

Figure 1. MSI Board Block Diagram

Note: The optional ring module is only applicable to the MSI/SC-R boards. Ringing SLICs (Subscriber Line Interface Circuits) provide the ringing function for the MSI/SC-Global and MSI/PCI-Global boards.

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