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P10501A08.DOC draft DSA Interface Description; Premium10501
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2. DSA-Interface
2.1 General description
For the DSA-interface implementation in the CD-module, it is practical to use a 16-bit structure. The 16
bits contain a COMMAND- and a DATA-byte are transmitted in one string, first the COMMAND-byte,
then the DATA byte. The meaning of the DATA-byte is determined by the COMMAND-byte. If the
COMMAND needs no DATA-byte, a dummy value will be transmitted.
The COMMAND and DATA byte will be sent with MSB first. All the DATA-bytes will be transmitted in
HEX-format.
Both processors can send COMMANDS to the other without asking for request. This means for example,
that the CD-module sends the new values to the User-processor every time the CD-time changes.
2.2 DSA-interface specification
The DSA-bus is an asynchronous, bi-directional, internal bus designed for communication between two
micro processors in one set. It consists of three bi-directional lines:
• DATA - for starting synchronisation and data transfer
• STB - for data strobe (DATA is valid while STB is low)
• ACK - for starting synchronisation, data transfer-acknowledge and
communication-acknowledge
DATA
STB
ACK
DATA
STB
ACK
User Processor Servo Processor
2.3 Description of communication
Each data communication consists of three phases:
• starting synchronisation synchronises the transmitter and the receiver for a data transmission
• data transmission the transmission of all data bits with the help of strobe and
acknowledge signals
• communication acknowledge the receiver lets the transmitter know whether the communication
was error free or not. If the communication was not error free, there
is a possibility to repeat it until it is OK
A processor is called a transmitter when it wants to transfer data, it starts with a synchronisation phase,
transfers the data and on request it receives finally the communication acknowledge.
The other processor becomes automatically the receiver.
