TDC-GP2 acam messelectronic gmbh, TDC-GP2 Datasheet - Page 20

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

Figure 8
f. Select input sensitivity
In register 2, Bits 19 & 20, RFEDGE1 and RFEDGE2,
the user can select whether the stop inputs are
sensitive to either rising or falling edges (RFEDGE =
"0") or to both rising and falling edges (RFEDGE = "1").
In register 0, Bits 0 to 2 the user can add an internal
inverter to each input, Start, Stop1 and Stop2. With
RFEDGE = "0" this is the same as rising edge (NEG_X =
"0") or falling edge (NEG_X = "1").
g. Interrupt behavior
The interrupt pin 8, INT can have different sources.
They are selected in register 2, Bits 21 to 23, EN_INT.
EN_INT = 0
The different options are wired by OR to enable more
than one source.
There are further configuration options that will be
described later in this chapter.
After the configuration the user has to initialize the
TDC-GP2 by sending opcode "Init" so that the TDC
accepts Start and Stop hits.
3.2.2 Measurement
After an initialization the TDC unit will start with the
first pulse on the Start input. It will run until:
- the set number of hits has been seen (maximum 4 on
both stop channels in measurement range 1)
- or until a timeout occurs at the end of the
measurement range (at 1.8µs in ,measurement range
1).
2xCal1-Cal2
measured
=offset
RES_X
1
2
4
time
Cal2
Cal1
acam-messelectronic gmbh - Am Hasenbiel 27 - D-76297 Stutensee-Blankenloch - Germany - www.acam.de
no Interrupt source
ALU ready
The set number of hits is there
Timeout of the TDC unit
forbidden
1xTref
time
2xTref
Cal2-Cal1
=gradient
time
real
20
The time measurement raw data are internally stored.
The number of hits can be seen from the status regis-
ter, bits 3 to 8.
In case calibration is active the TDC now measures one
and two periods of the internal reference clock (Tref *
1,2 or 4). The calibration raw data Cal1 and Cal2 are
also internally stored.
Figure 9
3.2.3 Data Processing
At the end of the measurement the ALU starts to
process the data according to the HIT1, HIT2 settings
and transfers the result to the output register. In case
calibration is off the ALU transfers the 16 Bit raw data
to the output register. With calibration the ALU
calculates according to 3.1.1.d and transfers the 32Bit
fixed point number to the output register.
The ALU can be switched off configuring HIT1=HIT2=5.
The time it takes the ALU depends on whether
calibration is on or not and the supply voltage.
Table 1: ALU timings
As soon as the data is available from the output
register the interrupt flag is set (assumed that the ALU
interrupt is enabled, see reg 2, EN_INT). Further the
load pointer of the output register is increased by 1
and points to the next free memory. The actual position
of the load pointer can be seen in the status register,
Bits 0 to 2.
3.2.4 Reading Data
Now the user can read the data sending the opcode
10110ADR. With the next 16 cycles (un-calibrated
data) or 32 cycles (calibrated data) the TDC-GP2 will
send the result, beginning with the most significant Bit
(MSB).
RefClk
Start
Stop
3.3 V
2.5 V
2.0 V
un-calibrated
220 ns
310 ns
580 ns
Cal1
3.2.1 Configuration
TDC-GP2
Cal2
calibrated
1.8 µs
2.5 µs
4.6µs