71m6403 Teridian Semiconductor Corporation, 71m6403 Datasheet - Page 48

• Manufacturer Part Number: 71m6403
• Description: Electronic Trip Unit
• Manufacturer: Teridian Semiconductor Corporation

Reset Mode: When the RESETZ pin is pulled low, all digital activity in the chip stops while analog circuits are still active.
Additionally, all I/O RAM bits are cleared..
When RESETZ goes high the MPU will begin executing its preboot and boot sequences from address 00. See the security
section for more description of preboot and boot.
As explained in the hardware section, the bits of the I/O RAM register CHOP_ENA[1:0] have to be toggled in between
multiplexer cycles to achieve the desired elimination of DC offset.
The amplifier within the reference is auto-zeroed by means of an internal signal that is controlled by the CHOP_EN bits. When
this signal is HIGH, the connection of the amplifier inputs is reversed. This preserves the overall polarity of the amplifier gain but
inverts the input offset. By alternately reversing the connection, the offset of the amplifier is averaged to zero. The function of the
two bits of the CHOP_EN register are described in Table 59.
For automatic chopping, the CHOP_EN bits are set to either 00 or 11. In this mode, the polarity of the signals feeding the
reference amplifier will be automatically toggled for each multiplexer cycle as shown in Figure 16. With an even number of
multiplexer cycles in each accumulation interval, the number of cycles with positive reference connection will equal the number
of cycles with reversed connection, and the offset for each sampled signal will be averaged to zero. This sequence is acceptable
when only the primary signals (circuit breaker voltage, circuit breaker current) are of interest.
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cycle 1
Positive
MUX
XFER_BUSY interrupt
Accumulation Interval m
CE_BUSY interrupt
versed
cycle 2
Chop Polarity
MUX
Re-
(falling edge)
(falling edge)
Positive
cycle 3
MUX
CHOP_EN[1]
0
0
1
1
Figure 16: Chop Polarity w/ Automatic Chopping
cycle n
versed
MUX
Re-
CHOP_EN[0]
Positive
cycle 1
MUX
©
2006 TERIDIAN Semiconductor Corporation
Fault, Reset, Power-Up
Table 59: CHOP_EN Bits
Accumulation Interval m+1
Chopping Circuitry
0
1
0
1
versed
Re-
Positive
Function
Toggle chop signal
Reference connection positive
Reference connection reversed
Toggle chop signal
cycle n
versed
MUX
Re-
Electronic Trip Unit
Positive
cycle 1
MUX
Accumulation Interval m+2
versed
Re-
Positive
71M6403
SEPTEMBER 2006
REV 1.0