ABB Symphony Harmony Series, Instruction, Page: 140 / 402

I/O Block
WBPEEUI240751C0 3 - 11
•
Status reporting.
Memory
The I/O block utilizes static-RAM memory and flash-ROM
memory. The static-RAM memory provides temporary storage
for the CPU to perform calculations and data manipulation.
The Hnet interface also uses a portion of the RAM memory to
store received messages and messages to be transmitted. The
flash-ROM memory stores the I/O block operating firmware
and the block’s portion of the control configuration. This type
of memory allows firmware upgrades to be downloaded from
the controller. The electronic ID of the block is stored in ROM
memory.
Hnet Interface
Hnet is the redundant, serial communication protocol over
which the Harmony controller communicates with I/O blocks.
Figure
3-9 details the Hnet interface section of the I/O module
circuitry. The Hnet interface encodes and transmits Hnet mes-
sages, receives and decodes Hnet messages, and monitors
Hnet status.
The Hnet control portion of the interface is a custom, applica-
tion-specific integrated circuit (ASIC). This circuit manages the
serial communication protocol between the I/O block and Har-
mony controller. It also performs data integrity checks. The
interface checks for the following message errors: Data trans-
mission error using cyclic redundancy check (CRC) method,
maximum message reply time expired, and reply message
overrun.
Figure 3-9. Hnet Interface
T R A N S C E IV E R
A
T R A N S C E IV E R
B
H N E T
C O N T RO L
R E L AY
A
R E L AY
B
H N E T A
H N E T B
T00 561B
DATA A N D
C O N T R O L