Md Mode Option (Factory Installed); Md Mode Description; Md Mode Enable - Serial Communication Mode; Md Mode Srq - Lambda Genesys GENH 750W Technical Manual

7.4 MD MODE OPTION (Factory Installed)

7.4.1 MD Mode Description

The GEN supply is capable of operating in a multi drop environment - more than 1 supply
conducting serial communications on a single serial bus. A maximum of 31 GEN supplies
can operate in this single bus. Upon power up the Gen will enter the point-to-point mode
in which it is assumed that only 1 supply will operate on a serial bus. MD Mode must be
enabled - Ref. Section 7.10.2.2. The user must set all Slave supplies to a unique address.
No two supplies may have the same address.
7.4.2 MD Mode enable – Serial communication mode
Refer to section 7.10.2.2. MD Mode is entered into via a Single byte command. In MD
Mode the Master supply shall operate in one of the two serial modes, RS232 or RS485,
depending upon the rear panel DIP switch setting and the Slave supplies shall operate in
the RS485 serial mode.

7.4.3 MD Mode SRQ

In MD Mode the SRQ generated by the supply is replaced by a single byte SRQ sent two
times in sequence. The SRQ byte, in binary, will contain the address of the supply in the
least significant 5 bits with bits 5 and 6 set to logic zero and bit 7 set to logic 1. Ref. Table
7-4.
7.4.4

Communication Collisions

In MD Mode it is possible to have one supply issue an SRQ while another supply is
transmitting data/response to a command. When this happens, the HOST PC will receive
garbled data and assume that the data/response was corrupted and thus re-send the
command - the SRQ will probably be lost. The method of recovery will be SRQ retrans-
mission, Ref. Section 7.4.5, or polling all attached supplies to see who issued the SRQ -
available by reading the SEVE? Register.

7.4.5 MD Mode SRQ Retransmission

The supply can be commanded to retransmit the SRQ at regular intervals until it is an-
swered to by the HOST PC (Ref. Section 7.10.2.4). The retransmission interval is 10 ms
plus the supply address multiplied by 20 ms.
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83-507-5002 Rev. A