Telemery Data Acqusition & Transmission System

Programmable Pulse Code Modulation (PPCM) Encoder

Programmable Pulse Code Modulation (PPCM) Encoder is a system uses the basic principle of Pulse Code Modulation (PCM), collects and encodes the data from various sub-systems in the missile to meet the telemetry requirement during flight of missile. The encoding mechanisms used in PPCM Encoder system are NRZ-L and Bi-phase-L.

PPCM Encoder acquires data for telemetry system from various interfaces. These interfaces include Analog inputs, Discrete inputs, MIL-STD-1553 bus and RS-422 serial links. Channel sampling is according to the IRIG standard. PPCM has a capability to change the control format through a PC via RS-422 port. The formatting information, when downloaded, is stored in EEPROM within the PPCM. The frame format information generates the necessary signals to address channels and select individual setup parameters for each channel of each module. The digitized data from each channel is then transmitted according to the format into the output serial data stream. Interfaces are provided for the input analog , discrete and digital channels.

The encoded serial data is signal conditioned through a pre-modulation filter and send to the next stage i.e. telemetry transmitter section.

The programmability is in terms of Bit rate, Frame length, Format Length and Frame sync. The programmability options will be provided through software.

Programmable Pulse Code Modulation (PPCM) Encoder functionality can be partitioned in to two parts.

	Data Acquisition
	PCM serial translation and transmission

Data acquisition meant for acquiring the data from various sources through 64 analog channels, 64 optoisolated channels, MIL-STD-1553 and RS-422 serial links and storing this data in a predefined locations. Micro controller is responsible for acquiring data from various channels and updating the data acquisition RAM.

Data stored in data acquisition RAM is transmitted out serially according to frame addressing defined in EEPROM. FPGA is responsible for taking the data from data acquisition RAM, converting it to serial form and sending out serially in NRZ-l and Bi-phase-L format.

The encoded serial data is signal conditioned through a pre-modulation filter and send to the next stage i.e. telemetry transmitter section. Programmability is provided for bit rate, frame rate, format rate and addressing through software.