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83
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507
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013 Rev. D
51
7.4 MD MODE OPTION (Factory Installed)
7.4.1 MD Mode Description
The GEN supply is capable of operating in a multi drop e
nvironment
-
more than 1 supply co
n
ducting
serial communications on a single serial bus. A maximum of 31 GEN supplies can operate in this si
n-
gle bus. Upon power up the Gen will enter the point
-
to
-
point mode in which it is a
s
sumed that only 1
supply will op
erate 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 en
tered into via a Single byte command. In MD Mode the Ma
s-
ter 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 s
e
rial 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 s
e-
quence. 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 a
s-
sume that the data/respons
e 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 pol
l
ing all attached
supplies to see who issued the SRQ
-
available by reading the SEVE? Regist
er.
7.4.5
MD Mo
de 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 address mult
i-
plied by 20 ms.