MCC iPort/USB 2, Руководство пользователя

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8
3 Hardware Configuration
3.1 Circuit Sense
™
The iPort/USB 2 introduces MCC’s Circuit Sense technology. Circuit Sense allow
the I
2
C intV wire can operate in two modes, Power Source Mode and
Voltage Sense Mode. Mode selection is controlled by the MODE slide switch on
the side of the unit enclosure.
• Power Source Mode - The +V wire can supply power (3.3v or 5v @ 100 mA)
Vcc to an external I
2
C Bus system. Voltage selection is controlled by the
SOURCE slide switch on the side of the unit enclosure. In Power Source Mode,
the voltage of the iPort/USB 2 SCL, SDA, and /INT internal pull-ups, if enabled,
and Voltage Sense circuit (0.3Vcc Low
MAX
, 0.7Vcc High
MIN
) is selected by the
SOURCE switch. (Use of the +V wire in Power Source Mode is user optional).
Power Source Mode is similar to the standard mode of operation on earlier
versions of MCC I
2
C Bus host adapters.
• Voltage Sense Mode - The +V wire is connected to the external I
2
C Bus system
pull-up supply voltage (0.5v to 5v) Vcc, and automatically adjusts iPort/USB 2
SCL, SDA, and /INT voltage sense circuit levels to match (0.3Vcc Low
MAX
,
0.7Vcc High
MIN
). In Voltage Sense Mode, the voltage of the iPort/USB 2 SCL,
SDA, and /INT internal pull-ups, if enabled, is equal to the external voltage
(Vcc) applied to the +V wire. (Use of the +V wire in Voltage Sense Mode is
required).
3.2 Pull-up Resistors
I
2
C Bus systems are based on open-collector technology requiring pull-up devices
on each signal wire (SCL, SDA, /INT). These pull-up devices usually take the form
of pull-up resistors connected to bus power.
The I
2
C adapter includes a PULL-UPS slide switch used to enable or disable
internal 1.8K ohm pull-up resistors attached to the SCL, SDA, and /INT lines.
Every I
2
C Bus system must have at least one pull-up on the signal lines. In some
cases, the pull-ups may be present in the external I
2
C Bus circuit. Use this switch to
configure the pull-up resistors for your system.