Specifications

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© 2002 UNIPOWER Corporation pcmi2c.p65 - rev b - 12/03/02
SPECIFICATIONS, PowerCassette
®
: I2C SERIAL BUS INTERFACE FOR PCM/TPCM
ELECTRICAL INTERFACE
OPERATION AND FUNCTIONS
Addressing (GA0, GA1 and GA2)
Three external address lines are employed allowing up to eight PowerCassette
modules to be addressed on a single I2C bus.
Module addressing is achieved through hard-wiring the address lines to
-Sense or the +5V auxiliary supply via a 100-ohm resistor on the system back-
plane. In this way it is the location or position of the module rather than any
particular module that is identified by an individual address.
Serial Clock (SCLK)
This line is clocked by the processor which controls the I2C serial bus. It
should be tied to +5V via a pull-up resistor in the range 3k to 10k.
Serial Data (SDA)
This line is a bidirectional data line. It should be tied to +5V via a pull-up
resistor in the range 3k to 10k.
Interrupt
This line provides an interrupt to the processor in the event of a change of
status of the digital register.
BUS speed
The I2C interface as used in PowerCassette is designed to run with a serial
clock speed 100kHz.
Digital Functions
Digital status functions are provided by a PCF8574 8-bit I/O port device.
When this device is read by the serial bus controller a single 8-bit word
provides the following information:
TIBNOITCNUF
DOOG
ETATS
GNINAEM
0liaFrewoPtupnI0 .eruliafylppustupnifogninrawsm01sedivorP
1
1dooGrewoPtuptuO0 .stimildeificepsnihtiwerasiV
2gninraWerutarepmeT1 .C06sdeecxeerutarepmetlanretnI
3dooG1#naF1 .deepslanimon%08>tagninnurnaF
4dooG2#naF1 .deepslanimon%08>tagninnurnaF
5dooG3#naF1 .deepslanimon%08>tagninnurnaF
6- - -
7mralAerutarepmeT1
.ffodehctiwstinu,C07sdeecxeerutarepmetlanretnI
.detavitcatibihnIdnaPVOsetacidnioslA
Note 1: AC input versions only.
TIB
76543210
EULAV
0100 2A1A0AW/R
PCF8574 slave address
Note: If a zero is written to bit 7 in a data byte, the unit will be inhibited. The default state is
enabled.
EEPROM Functions
The EEPROM is a 2048 bit (256 byte) device which is preprogrammed at the
factory with the following data:
EGNARSSERDDAATAD
51-0rebmuNledoM
13-61rebmuNtraPgnirutcafunaM
74-23rebmuNlaireS
36-84leveLnoitacifidoM
97-46rerutcafunaM
59-08erutcafunaMfoyrtnuoC
552-69desutoN
Note:
Data is organized such that each
field of data can be accessed by a
page read (16 bytes).
TIB
76543210
EULAV
10 10 2A1A0AW/R
EEPROM slave address
Note: Customers may specify to special order other data which they may require.
Temperature Measurement Functions
The internal temperature of the unit is measured using a MAX6633. This
device provides a 12-bit measurement at a resolution of 0.0625°C.
TIB
76543210
EULAV
1000 2A1A0A0
MAX6633 slave address
Note: The MAX6633 must only be used in the READ mode.
Analogue Functions
Analogue status functions are provided by two PCF8591 4-channel 8-bit A/
D converter devices. When these devices are read by the serial bus
controller a single 8-bit word provides the following information:
1U:eciveD
D/ANOITCNUFD/ANOITCNUF
1egatlovV3desuton
2tnerrucV4desuton
TIB
76543210
eciveD
EULAV
100 1 2A1A0AW/R
1U
Slave addresses
The PCF8591 devices initially require a control byte (04 Hex) to be written
to the configuration register. This control byte sets the device so that on
each successive read the data from the next A/D is read. Note that on each
read a conversion is started for a particular channel and the result will be
read from the previous channel, thus the first result from a sequence of reads
should always be discarded.
A/D converter scaling
To obtain a correct voltage or current measurement it is necessary to employ
both scaling and offset factors in the controlling software. Note that all
voltage measurements are made inside the PSU module, before the ‘ORing’
diodes, and are typically 0.5V higher than the actual module output voltage.
The following calculation should be employed:
Value = (byte read x scaling factor) + offset
egatloVtuptuOgnilacSecnareloTtesffO
V219160.0%2±0
)1D/A1U(egatloVV
V42%2±0
V84%2±0
V21262.0*%01±0
)2D/A1U(tnerruCV
V42*%01±0
V84*%5±0
* of full scale