TDC-GP2 acam messelectronic gmbh, TDC-GP2 Datasheet - Page 23

• Manufacturer Part Number: TDC-GP2
• Description: Precision Time Interval Measurement
• Manufacturer: acam messelectronic gmbh

4.1 Measurement Flow
Figure 12
4.1.1 Configuration
At the beginning the TDC-GP2 has to be configured.
The main settings for measurement range 2 are:
a. Select measurement range2 setting register 0,
Bit3, MRange2 = 1.
b. Select the reference clock (see also section 5.1)
In measurement range 2 the TDC-GP2 needs the high-
speed clock for the time measurement. In case of low-
power applications this clock can be switched of in
between measurements. The a 32.768 kHz clock is
necessary for the timing control during the oscillator
power-on.
Register 0, Bits 10&11, START_CLKHS defines the
switch-on behavior of the high-speed clock. If only the
high-speed clock is used this is be set to
"1"(continuously on). In case both oscillators are used
for current saving reasons this should be set to "2" for
ceramic oscillators and to "3" for quartz oscillators".
Register 0, Bits 12&13, ClkHSDiv sets an additional
internal divider for the reference clock (1,2 or 4). The
choice has an influence on the minimum time interval
and the maximum time interval
t
t
Configuration
-Mode
-How many hits per Chan.
-Clock
-Calibration
TDC unit waits for
-Start pulse
-Stop pulse(s)
ALU postprocessing
according to
HIT1&HIT2
min
max
2
2
Calibration
measurement
14
Initialization
T
Interrupt
ref
T
acam-messelectronic gmbh - Am Hasenbiel 27 - D-76297 Stutensee-Blankenloch - Germany - www.acam.de
ref
2
ClkHSDiv
2
ClkHSDiv
3.1.2
3.1.3
timeout
3.1.1
3.1.1
3.1.2
3.1.3
.
one stop
only
Read Data
Read Data 3.1.4
Write
new value into
HIT1 & HIT2
more than
one stop
3.1.4
3.1.4
23
It is necessary that
the ALU will go into an overflow during calibration and
write 0xFFFFFFFF as output data.
c. Set the number of expected hits
In register 0, Bits 8 to 10, HITIN1 the user has to
define the number of hits the TDC-GP2 has to wait for.
A maximum of 3 on channel 1 is possible. The number
HITIN1 always has to be higher by 1 than the number
of expected hits. The reason is that the Start is also
counted as a hit. The TDC-GP2 measures until the set
number of hits is registered or a timeout occurs.
register 0, Bits 11 to 13, HITIN2 have to be set to "0".
Example:
2 stop pulses are expected:
HITIN1 = 3, HITIN2 = 0
d. Select calibration
The calibration is switched on by setting register 0,
Bit5, Calibrate = "1". It is mandatory to do this.
For the calibration the TDC measures 1 and 2 cycles of
the reference clock. The two data are stored as Cal1
and Cal2.
There are two ways to update the calibration data Cal1
and Cal2:
- Separate calibration by sending opcode
Start_Cal_TDC via the SPI interface
- Automatic update by setting register 0, Bit 4,
DisAutoCal = "0". In most applications this will be the
preferred setting.
e. Define ALU data processing
While the TDC unit can measure up to 3 hits the ALU
can calculate only one hit at once. The settings are
done in register 1, Bits 16 to 19 and 20 to 23, HIT1
and HIT2. The Start pulse is internally handled like a
Stop pulse because of the special measuring method in
measurement range 2.
Reg1 = 0x21xxxx
Reg1 = 0x31xxxx
Reg1 = 0x41xxxx
The ALU calculates the time interval as:
RES
Time
_
X
RES
CoarseCoun
_
X
T
ref
1
2
3
2
t
2
s t
n d
r d
ClkHSDiv
Stop Ch1-Start
Stop Ch1-Start
Stop Ch1-Start
T
HIT
Cal
ref
1
2
2
HIT
ClkHSDiv
Cal
4.1 Measurem ent F l ow
2
1
TDC-GP2
1
8 .
s
. Otherwise