TC815CBU View Datasheet(PDF) - Microchip Technology
Part Name
Description
Manufacturer
TC815CBU
Microchip Technology
TC815CBU Datasheet PDF : 26 Pages
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TC815
6.0 -MEM OPERATING MODE
Bringing -MEM (Pin 61) momentarily low configures the
TC815 “-MEM” Operating mode. The -MEM LCD
Annunciator becomes active. In this Operating mode,
subsequent measurements are made relative to the last
two digits (-99) displayed at the time MEM is low. This
represents 5% of full scale. The last two significant digits
are stored and subtracted from all the following input
conversions. The following examples clarify operation:
EXAMPLE 6-1: IN AUTO-RANGING
RI (N) = 18.21kΩ (20kΩ Range) = > Display 18.21kΩ
MEM
= > Store 0.21kΩ
RI (N+1) = 19.87kΩ (20kΩ Range)
= > Display 19.87 - 0.21 = 19.66kΩ
RI (N+2) = 22.65kΩ (200kΩ Range)
= > Display 22.7kΩ and MEM disappears
EXAMPLE 6-2:
IN FIXED RANGE
(200.0Ω FULL SCALE)
RI (N) = 18.21kΩ = > Display 18.2kΩ
MEM
= > Store 8.2Ω
RI (N+1) = 36.7Ω
= > Display 36.7 - 8.2 = 28.5Ω
RI (N+2) = 5.8Ω
= > Display 5.8 = 2.4Ω*
*Will display minus resistance if following input is
less than offset stored at fixed range.
EXAMPLE 6-3: IN FIXED RANGE
VI (N) = 0.51V = > Display 0.51V
MEM
= > Store 0.51V
VI (N+1) = 3.68V
= > Display 3.68 - 0.51 = 3.17V
VI (N+2) = 0.23V
= > Display 0.23 - 0.51 = -0.28V
VI (N+3) = -5.21V
= > Display - 5.21 - 0.51 = -5.72V
On power-up, the TC815 “-MEM” mode is not active.
Once the “-MEM” is entered, bringing MEM low again,
it returns the TC815 to normal operation.
The “-MEM” mode is also cancelled whenever the mea-
surement type (resistance, voltage, current AC/DC,
Ω/LOΩ) or range is changed. The LCD -MEM annunci-
ator will be off in normal operation.
In the auto-range operation, if the following input signal
cannot be converted on the same range as the stored
value, the “-MEM” mode is cancelled. The LCD annun-
ciator is turned off.
The “-MEM” Operating mode can be very useful in
resistance measurements when lead length resistance
would cause measurement errors.
DS21474B-page 14
7.0 AUTOMATIC RANGE
SELECTION OPERATION
When power is first applied, the TC815 enters the auto-
range operating state. The Auto-Range mode may be
entered from Manual mode by changing the measure-
ment function (resistance or voltage), or by changing
the measurement option (AD/DC, Ω/LOΩ).
The automatic voltage range selection begins on the
most sensitive scale first: 200mV for DC or 2.000V for
AC measurements. The voltage range selection flow
chart is given in Figure 7-1.
Internal input protection diodes to VDD (Pin 28) and
VSSA (Pin 57) clamp the input voltage. The external
10MΩ input resistance (see Figure 7-1, R14 and R13)
limits current safely in an overrange condition.
The voltage range selection is designed to maximize
resolution. For input signals less than 9% of full scale
(count reading <180), the next most sensitive range is
selected.
An over range voltage input condition is flagged when-
ever the internal count exceeds 2000, by activating the
buzzer output (Pin 4). This 4kHz signal can directly
drive a piezo electric acoustic transducer. An out of
range input signal causes the 4kHz signal to be on
122msec, off for 122 msec, on for 122msec and off for
610msec (see Figure 11-1).
During voltage auto-range operation, the extended res-
olution feature operates on the 2000V range only. (See
Extended Resolution Operating mode discussion.)
The resistance automatic range selection procedure is
shown in Figure 7-2. The 200Ω range is the first range
selected unless the TC815 low ohms resistance mea-
surement option is selected. In low ohms operation, the
first full scale range tried is 2kΩ.
The resistance range selected maximizes sensitivity. If
the conversion results in a reading less than 180, the
next most sensitive full scale range is tried.
If the conversion is less than 19 in auto-range opera-
tion, a continuous 4kHz signal is output at BUZ (Pin 4).
An over range input does not activate the buzzer.
Out of range input conditions are displayed by a blink-
ing most significant digit with the three least significant
digits set to “000.”
The extended resolution feature operates only on the
2000kΩ and 2000V full scale range during auto-range
operation. A blinking “1” most significant digit is inter-
preted as the digit 2. The three least significant digits
display data normally.
© 2002 Microchip Technology Inc.
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