83-507-013 Rev. A
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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 con-
ducting serial communications on a single serial bus. A maximum of 31 GEN supplies can oper-
ate in this single bus. Upon power up the Gen will enter the point-to-point mode in which it is as-
sumed 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 retransmission, Ref. Section 7.4.5, or poll-
ing all attached supplies to see who issued the SRQ - available by reading the SEVE? Registe
r.
7.4.5 MD Mode SRQ Retransmission
The supply can be commanded to retransmit the SRQ at regular intervals until it is answered to
by the HOST PC (Ref. Section 7.10.2.4). The retransmission interval is 10 ms plus the supply ad-
dress multiplied by 20 ms.
