18/09/2003
HESC-UPS Manual
Tri-M Engineering
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9
4b. Read command with checksum acknowledge.
HOST: <addressR> <command> <0x02> <0x03> <0xFF>
HESC104: [0x00] [databyteR low] [databyteR high] [checksum]
where "host" addressW = 0001 001 + 0 (R/W bit) = 0x12
"host" addressR = 0001 001 + 1 (R/W bit) = 0x13
The checksum is a two digit hexadecimal checksum that is the two's complement of the sum of all preceding bytes. For
example the data <0x10> <0x12> <0xC0> <0x03> has the checksum 0x1B.
Section 5 : HESC I
2
C/SMBus Bus Communications
A. Description:
The HESC can communicate with System Management Bus (SMBus) batteries, I
2
C digital temperature sensors, and
Hosts and microprocessors through the I2C/SMBus. The SMBus is a two-wire interface through which the HESC can
communicate to I
2
C/SMBus devices. The HESC supports I
2
C/SMBus multi-master bus capability, meaning that other
devices capable of controlling the bus can be connected to it. The HESC transfers data by one I
2
C/SMBus device acting
as a master, and another I
2
C/SMBus device acting as a slave (with one of the devices being the HESC). A master device
initiates a bus transfer and provides the clock signals (SCL). A slave device can receive data (SDA) provided by the
master or it can provide data to the master. Since more than one device may attempt to take control of the bus as a
master, I
2
C/SMBus provides an arbitration mechanism, relying on the wired-AND connection of all I
2
C/SMBus interfaces
to the I
2
C/SMBus.
NOTE:
Care should be taken in the design of both the input and output stages of SMBus devices, in order
not to load the bus when their power plane is turned off.
The HESC uses the master to alert the Host of a change in status or of alarm in the HESC. The HESC alerts the Host by
sending the ChargerStatus() value. This occurs when main power is applied or removed, battery pack inserted/removed,
battery fully charged or fully discharge, shutdown activated or de-activated, or temperature alarm. When the HESC
alerts the Host, the HESC places its address 0x12 in the command byte. The HESC alert communications format would
then appear as 0x10, 0x12, datalow, datahigh.
- Table 1 lists the commands the HESC I
2
C/SMBus supports.
To ensure reliable communication, an acknowledge bit is returned after each address, command or data byte transmitted.
The receiving device must acknowledge receipt of each byte. If an acknowledge bit is not received then the transfer is
aborted immediately and the result byte set accordingly.
Section 6 SerBus, SMBus, and PC/104 Command Functions
A. List of Command Functions
1. The SerBus and PC/104 Bus command functions are similar to many of the SMBus command functions. Where
possible, the functions are the same as the SMBus functions. The following table list the HESC command functions,
access, units and range of the data.
2. There are two types of command functions, RAM and EEprom. RAM variables are used to actively monitor and
control the HESC. However, RAM is volatile memory and loses it contents on power loss. The EEprom is used to
store setpoints and configuration for the HESC. Separate functions allow easy access to the RAM variables.
