555299748ee_36| Application Note
Engineer To Engineer Note
EE-36
Notes on using Analog Devices' DSP, audio, & video components from the Computer Products Division Phone: (800) ANALOG-D or (781) 461-3881, FAX: (781) 461-3010, EMAIL: dsp.support@analog.com
ADSP-21xx interface to the IOM-2 bus
Last Modified: 7/23/97
The IOM-2 terminal version consists of three subframes, each containing 32 bits. This 12 byte frame is repeated at 8kHz, giving an aggregate data rate of 768kbit/s.
Introduction
The IOM Revision 2 ( IOM-2 ) standard defines an industry standard serial bus for interconnecting telecommunications ICs. The serial interface satisfies the requirements of ISDN and analog applications and has been defined by four major European telephone equipment manufacturers.
ADSP-21xx Serial Port
The ADSP-21xx has one/two synchronous serial fullduplex 5 wire ports (SPORT) and one of these interfaces supports time-multiplexed data streams. Data is clocked by the Serial Clock (SCLK) that operates at the data rate. Optional there is a Frame Sync Signal for the receive & transmit side that indicates the start of a new word or frame in multichannel mode. Data is sent over Data Transmit (DT) and Data Receive (DR) lines. In normal operation an interrupt is generated when an word has been received or when a transmitted word has been shifted out of the SPORT. There are two independent interrupt vector locations to handle the receiving and transmitting section separately.
The IOM-2 Bus
The IOM-2 bus is a synchronous full duplex communication link, containing user data, control/programming, and status channels and has been designed for terminal mode and line card mode. Both the line card mode and terminal portions of the IOM-2 standard utilize the same basic frame and clocking structure, but differ in the number and usage of the individual channels that are time-multiplexed over a fourwire serial interface. Data is clocked by a Data Clock (DCL) that operates at twice the data rate. A frame is delimited by an 8-kHz Frame Synchronization Clock (FSC). Data is transmitted over Data Upstream (DU) and Data Downstream (DD).
Autobuffering
The generation of an interrupt after each transmitted/ received word would cause a huge overhead and for this reason you could use an autobuffering mode that automatically transfers SPORT data to/from the internal memory of the DSP. For this application you have to define a circular buffer in the internal memory that should hold the data to be sent/received. The length of the buffer is user defined and when the buffer is full or has been read completely an interrupt will be generated and the buffer will be filled/ read again by the SPORT. This means we have to process the data in the buffer before the SPORT accesses this memory again.
Line Card Mode
The line card version of the IOM-2 provides a connection path between line transceivers (ISDN) and codecs (analog), and the line card controller; the line card controller provides the connection to the switch backbone. In this mode up to 8 ISDN transceiver or up to 16 codecs/filters could be connected to the bus. Data, control and status information is multiplexed into frame, which are transmitted in an 8kHz rate. The frames are divided into 8 sub-frames, with one sub-frame being dedicated to each transceiver or pair of codecs.
Multichannel Mode
As already mentioned above one of the SPORTs of the DSP has the possibility to handle time-multiplexed data streams. It is possible to choose between 24 or 32 time slots. The user can define in which time slots he wants to send data and which time slots should be ignored during reception. This can be done independently for the receiving & and transmitting side. The autobuffering mode could also be combined with the MC mode. The best way to combine autobuffering and multichannel mode is to set the length of the circular autobuffer to the number of time slots that should be sent/ received. In the following
Terminal Mode
The Terminal Mode is designed for ISDN and NT1 applications.
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