Rainbow Electronics LM41 - Manual (Page 12)

1.0 Functional Description
(Continued)
1.3.2 Read Transaction
During a read transaction, the master reads data from a
register at a specified address within a slave. A read trans-
action begins with a Start Bit and ends with an ACK bit, as
shown in Figure 5.
• Device Number This is the address of the LM41 device
accessed. Address "000" is a broadcast address and can
be responded to by all the slave devices. The LM41
ignores the broadcast address during a read transaction.
• Internal Address The address of a register within the
LM41 that is read.
• Read/Write (R/W) A "1" indicates a read transaction.
• Data Bits During a read transaction the data bits are
driven by the LM41. Data is transferred serially with the
most significant bit first. This allows throughput optimiza-
tion based on the information that needs to be read.
The LM41 supports 8-bit or 16-bit data fields, as de-
scribed in Section 2.0 "Register Set".
• Even Parity (EP) This bit is based on all preceding bits
(device number, internal address, Read/Write and data
bits) and the parity bit itself. The parity -number of 1’s - of
all the preceding bits and the parity bit must be even - i.e.,
the result must be 0. During a read transaction, the EP bit
is sent by the LM41 to the master to allow the master to
check the received data before using it.
• Acknowledge (ACK) During a read transaction the ACK
bit is sent by the master indicating that the EP bit was
received and was found to be correct, when compared to
the data preceding it, and that no conflict was detected
on the bus (excluding Attention Request - see Section
1.3.5 "Attention Request Transaction"). A read transfer is
considered "complete" only when the ACK bit is received.
A transaction that was not positively acknowledged is not
considered "complete" by the LM41 and following are
performed:
— The BER bit in the LM41 Device Status register is set
— The LM41 generates an Attention Request before, or
together with the Start Bit of the next transaction
A transaction that was not positively acknowledged is
also not considered "complete" by the master (i.e. inter-
nal operations related to the transaction are not per-
formed). The transaction may be repeated by the master,
after detecting the source of the Attention Request (the
LM41 that has a set BER bit in the Device Status regis-
ter). Note that the SensorPath protocol neither forces, nor
automates re-execution of the transaction by the master.
The values of the ACK bit are:
— 1: Data was received correctly
— 0: An error was detected (no-acknowledge).
1.3.3 Write Transaction
In a write transaction, the master writes data to a register at
a specified address in the LM41. A write transaction begins
with a Start Bit and ends with an ACK Data Bit, as show in
Figure 6.
• Device Number This is the address of the slave device
accessed. Address "000" is a broadcast address and is
responded to by all the slave devices. The LM41 re-
sponds to broadcast messages to the Device Control
Register.
• Internal Address This is the register address in the
LM41 that will be written.
• Read/Write (R/W) A "0" data bit directs a write transac-
tion.
20070308
FIGURE 4. Bus Reset Transaction
20070309
FIGURE 5. Read Transaction, master reads data from LM41
LM41
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