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Users Manual & Installation Guide
PV- 5127: Power supply module with UPS
Page 23 of 31
The ATX on/off state machine
The ATX on/off state machine has two states: ATX_OFF and ATX_ON. Only in the ATX_ON
state can the 5V+12V outputs be turned on.
The state machine is controlled by the PS_ON input (located in the CN10 connector), and the
system temperature status. PS_ON is active low – it is active when pulled low to 0V, and inactive
when high or left floating.
• The state machine starts up in ATX_OFF when the main DC/DC converter starts.
• It changes to ATX_ON when PS_ON is active and the system temperature is OK (cool or
warm). This means that the CPU cannot turn itself on when the temperature is not OK (too
cold or too hot).
• It stays in ATX_ON as long as PS_ON is active. Even if the system temperature becomes
too cold or too hot, it stays in ATX_ON, as long as PS_ON is active. This means that the
CPU won’t suddenly be turned off if the temperature becomes bad (but it can decide to do a
controlled shutdown and power off when it sees the temperature status).
• When PS_ON goes inactive, it changes to ATX_OFF.
If your CPU cannot control the PS_ON input, you can make it permanently active by placing a
jumper in CN10.
The Softoff state machine
The Softoff state machine is intended for use with UPS monitoring software, such as the Windows
2000/XP UPS service. The Softoff state machine is controlled by the RS232 Shutdown (DTR)
signal, the system temperature status, and software commands through the PC/104 bus. This state
machine is useful when your CPU does not support the PS_ON signal. With this state machine, you
can perform a shutdown using an RS232 handshake signal (see the section RS232), and through a
software command through the PC/104 bus (see the section PC/104 Interface). If you leave the
RS232 DTR unconnected, it is by default inactive.
The state machine has four states: SOFT_ON, SOFT_DELAY, SOFT_OFF and
SOFT_TEMPBAD. SOFT_ON and SOFT_DELAY are the “on” states, i.e. only in these states can
the 5V+12V be turned on. SOFT_OFF and SOFT_TEMPBAD are the “off” states, where the
5V+12V is guaranteed to be off.