TDC-GP2 acam messelectronic gmbh, TDC-GP2 Datasheet - Page 24

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

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.
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.
4.1.2 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 3 on
channel 1 in measurement range 2)
- or until a timeout occurs. The timeout can be
programmed in multiples of the reference clock setting
Reg 3, Bits 19&20, SEL_TIMO_MR2. At 4 MHz the
values are:
SEL_TIMO_MR2 (@ 4 MHz, ClkHSDiv = 0)
At the end of the time measurement the TDC
measures 2 periods of the reference clock for
calibration.
4.1.3 Data processing
At the end of the measurement the ALU starts to
process the data according to the HIT1, HIT2 settings
= 0
= 1
= 2
= 3
1
2
4
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
2
2
2
2
10
12
14
8
T
T
T
T
ref
ref
ref
ref
2
2
2
2
ClkHSDiv
ClkHSDiv
ClkHSDiv
ClkHSDiv
= 64 µs
= 256 µs
= 1024 µs
= 4096 µs
24
and transfers the result to the output register. The
ALU calculates according to 4.1.2.e and transfers the
32Bit fixed point number to the output register.
The time it takes the ALU depends on the supply
voltage:
Table 2: 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.
4.1.4 Reading Data
Now the user can read the data sending the opcode
10110ADR. With the next 32 cycles (calibrated data)
the TDC-GP2 will send the result, beginning with the
main significant Bit (MSB).
The 32 Bit fixed-point number in complements of 2
represent the time interval in multiples of the
reference clock.
The configuration of the ALU allows only one hit
calculation at the time. In case more than one hit has
been measured it is necessary to write new commands
to HIT1/HIT2 to instruct the ALU for calculating the
other hits. After writing to HIT1/HIT2 it is necessary to
wait for minimum 4.6µs (calibrated data) or 580ns (un-
calibrated data) before reading or writing again to
HIT1/HIT2.
Example:
configuration
...
write reg1=0x214400
Hit1-Start
...
Initialize
...
while(Check interrupt flag)
write reg1=0x314400
wait(4.6µs)
write reg1=0x414400
wait(4.6µs)
Time
3.3 V
2.5 V
2.0 V
RES
_
X
T
ref
2
ClkHSDiv
1.8 µs
2.5 µs
4.6µs
'3 hits on channel 1, calculate
calculate Hit2-Start
calculate Hit3-Start
,
4.1.1 Configuration
TDC-GP2