Rainbow Electronics 71M6542G - Manual (Page 22)

22 © 2008–2011 Teridian Semiconductor Corporation v1.1
2.2.8 71M6x01 Isolated Sensor Interface (Remote Sensor Interface)
2.2.8.1 General Description
Non-isolating sensors, such as shunt resistors, can be connected to the inputs of the 71M654x via a
combination of a pulse transformer and a 71M6x01 IC (a top-level block diagram of this sensor interface
is shown in
Figure 36 ). The 71M6x01
receives power directly from the 71M654x via a pulse transformer
and does not require a dedicated power supply circuit. The 71M6x01 establishes 2-way communication
with the 71M654x, supplying current samples and auxiliary information such as sensor temperature via a
serial data stream.
One 71M6x01 Isolated Sensor can be supported by the 71M6541D/F and 71M6542F. When remote
interface IBP-IBN is enabled, the two analog current inputs pins IBP and IBN become a digital balanced
differential interface to the remote sensor. See
Table 3 for details.
Each 71M6x01 Isolated Sensor consists of the following building blocks:
• Power supply for power pulses received from the 71M654x
• Digital communications interface
• Shunt signal pre-amplifier
• Delta-Sigma ADC Converter with precision bandgap reference (chopping amplifier)
• Temperature sensor
• Fuse system containing part-specific information
During an ordinary multiplexer cycle, the 71M654x internally determines which other channels are
enabled with MUX_DIV[3:0] (I/O RAM 0x2100[7:4]). At the same time, it decimates the modulator output
from the 71M6x01 Isolated Sensors. Each result is written to CE RAM during one of its CE access time
slots. See
Table 3 for the CE RAM locations of the sampled signals.
2.2.8.2 Communication between 71M654x and 71M6x01 Isolated Sensor
The ADC of the 71M6x01 derives its timing from the power pulses generated by the 71M654x and as a
result, operates its ADC slaved to the frequency of the power pulses. The generation of power pulses, as
well as the communication protocol between the 71M654x and 71M6x01 Isolated Sensor is automatic and
transparent to the user. Details are not covered in this data sheet.
2.2.8.3 Control of the 71M6x01 Isolated Sensor
The 71M654x can read or write certain types of information from each 71M6x01 isolated sensor.
The data to be read is selected by a combination of the RCMD[4:0] and TMUXRn[2:0]. To perform a read
transaction from one of the 71M6x01 devices, the MPU first writes the TMUXRn[2:0] field (where n = 2, 4, 6,
located at I/O RAM 0x270A[2:0], 0x270A[6:4] and 0x2709[2:0], respectively). Next, the MPU writes
RCMD[4:0] (SFR 0xFC[4:0]) with the desired command and phase selection. When the RCMD[4:2] bits
have cleared to zero, the transaction has been completed and the requested data is available in
RMT_RD[15:0] (I/O RAM 0x2602[7:0] is the MSB and 0x2603[7:0] is the LSB). The read parity error bit,
PERR_RD (SFR 0xFC[6]) is also updated during the transaction. If the MPU writes to RCMD[4:0] before a
previously initiated read transaction is completed, the command is ignored. Therefore, the MPU must wait
for RCMD[4:2]=0 before proceeding to issue the next remote sensor read command.
The RCMD[4:0] field is divided into two sub-fields, COMMAND=RCMD[4:2] and PHASE=RCMD[1:0], as
shown in
Table 5 .
Table 5. RCMD[4:0] Bits
Command
RCMD[4:2] Phase Selector
RCMD[1:0]
Associated TMUXRn
Control Field
000 Invalid 00 Invalid ---
001 Command 1 01 IBP-IBN TMUXRB [2:0]
100 Reserved
101 Invalid
110 Reserved