TDC7200: Values in TIME2 to TIME6 Registers

Ahmed Kamel

Part Number: TDC7200
Other Parts Discussed in Thread: TDC1000,

Hello, i am implementing a water flow meter using TDC1000 and TDC7200. The value in TDC7200 TIME1 register is stable as well as the other registers, however the values in TIME2 through TIME6 registers have a big deviation and sometimes exceed the value in TIME1 giving a minus value which affects the TOF result.

What is the cause of this problem?

Thank you

over 8 years ago

0 Vishy Viswanathan over 8 years ago

TI__Mastermind 21685 points

Please share register settings of TDC7200. Are you using Mode 2 or Mode 1? Are you using 5 stops?

0 Ahmed Kamel over 8 years ago in reply to Vishy Viswanathan

Intellectual 935 points

TDC7200_CONFIG1_REG, 0x02
TDC7200_CONFIG2_REG, 0x44
TDC7200_INTRPT_MASK_REG, 0x01
TDC7200_COARSE_COUNTER_OVH_REG, 0xFF
TDC7200_COARSE_COUNTER_OVL_REG, 0xFF
TDC7200_CLOCK_COUNTER_OVH_REG, 0xFF
TDC7200_CLOCK_COUNTER_OVL_REG, 0xFF
TDC7200_CLOCK_COUNTER_STOP_MASKH_REG, 0x00
TDC7200_CLOCK_COUNTER_STOP_MASKL_REG, 0x00

0 Vishy Viswanathan over 8 years ago in reply to Ahmed Kamel

TI__Mastermind 21685 points

You are using Mode 2 and 5 stops. So in TIME2 to TIME6 registers, TDC7200 reports the number of ring oscillator cycles between the corresponding stop edge and the next clock edge. See Figure 18 of the data sheet. This duration can be greater than the value in TIME1 register.
In other words, TIME1 - TIMEx, where x = 2 to 6 can be negative.

Thanks,
Vishy

0 Ahmed Kamel over 8 years ago in reply to Vishy Viswanathan

Intellectual 935 points

So, should i take the absolute value of the result? What is the indication of the negative value?
Thank you

0 Vishy Viswanathan over 8 years ago in reply to Ahmed Kamel

TI__Mastermind 21685 points

Please refer Figure 18: TIME1 is occurence of START edge to first clock edge. TIME2 is occurence of STOP1 edge to next clock edge. These are asynchronous events. So TIME2 value can be greater than TIME1 and in that case it has be subtracted to get the correct time. You cannot use absolute value. TIME1 - TIME2 is negative it means START happened closer to first clock edge compared to STOP1 duration to next clock edge.
Thanks,
Vishy

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TDC7200: Values in TIME2 to TIME6 Registers