Research & Development
SPI-Interface
Specifications
for SPOT
CDS500D & CDS550D
OEM
Capacitance Diaphragm
Sensors
V 1.1
November 10, 2014
SPOT CDS500D & CDS550D OEM Sensor SPI-Interface Specification_V1.1 Page 1 of 14
Christian Berg, T based on Felix Mullis, TL Created 11/10/2014 2:36:00 PM
Research & Development
1 Table of Contents
1 Table of Contents ............................................................................................................. 2
2 Hardware Concept ............................................................................................................ 3
2.1 Hardware Block Diagram ............................................................................................................... 3
2.2 Interface Connector and Cable ...................................................................................................... 4
2.3 Grounding Concept ........................................................................................................................ 4
2.4 Timing Specifications ..................................................................................................................... 4
2.5 Interface Hardware Specifications ................................................................................................. 5
2.5.1 Power Supply .......................................................................................................................... 5
2.5.2 Recommended operating conditions....................................................................................... 5
2.5.3 SPI Interface ............................................................................................................................ 6
3 Read Results ..................................................................................................................... 7
3.1 Pressure ......................................................................................................................................... 7
3.2 Temperature .................................................................................................................................. 8
3.3 Status and Error ............................................................................................................................. 9
3.4 Power-up reset ............................................................................................................................... 9
4 History ............................................................................................................................... 9
5 Appendix ..........................................................................................................................10
5.1 Grounding Concepts .................................................................................................................... 10
5.2 SPI Timing ................................................................................................................................... 11
5.2.1 Introduction ............................................................................................................................ 11
5.2.2 Timing .................................................................................................................................... 11
5.2.3 Total Measurement Cycle ..................................................................................................... 12
5.2.4 Ready-signal ......................................................................................................................... 12
5.2.5 Single Measurement Cycle ................................................................................................... 13
5.2.6 Readout Time Window .......................................................................................................... 13
5.2.7 Conclusion ............................................................................................................................. 14
5.2.8 FAQ’s, Comments ................................................................................................................. 14
SPOT CDS500D & CDS550D OEM Sensor SPI-Interface Specification_V1.1 Page 2 of 14
Christian Berg, T based on Felix Mullis, TL Created 11/10/2014 2:36:00 PM
Research & Development
2 Hardware Concept
This section describes how two or more SPOT CDS5xxD slaves must be physically connected together with a master. When doing so, the master will be able to receive pressure and temperature data
from each SPOT CDS5xxD slave.
The data exchange link consists of a simple SPI-Interface; therefore only three lines and a chip select
signal are necessary. The additional RDY/ lines signal the end of a measurement cycle. It must be
used in noise critical applications. There it’s forbidden to read data from the chip during measurement
cycles. (Crosstalk from the SPI-interface to the measurement data)
2.1 Hardware Block Diagram
Figure 2.1-1: SPI Block Diagram
SPOT CDS500D & CDS550D OEM Sensor SPI-Interface Specification_V1.1 Page 3 of 14
Christian Berg, T based on Felix Mullis, TL Created 11/10/2014 2:36:00 PM
Research & Development
Direction
Signal
Description
MIN TYP MAX
UNIT
2.2 Interface Connector and Cable
Connector Type: JST 1mm 10 pol.
pin Signal Description
1 +5V Power Supply input
2 GND Supply Common input
3 Clk SPI Clock input
4 SS/ SPI Slave Select (low true) input (low true)
5 MISO SPI Master Input Slave Output output (tristate)
6 MOSI SPI Master Output Slave Input input
7 RDY/ Ready Signal (new measurement value available) output (low true)
8 C1/C0 Internal use only, must be left open output
9 R0/Rref Internal use only, must be left open output
10 Vpp_OTP
Cable length: max. 15 cm
Internal use only, must be left open input
Table 1: pin assignment SPI connector
(SPOT CDS5xxD-side)
2.3 Grounding Concept
The metallic sensor housing (flange) acts as a shielding for the very sensitive electronic measurement
frontend. In order to achieve the specified noise specifications, the sensor flange must be connected
to GND (Supply Common). The impedance of such a connection should be as low as possible. Therefore it is realized directly on the PCB at the frontend of the electronics. This solution guarantees lowest
noise and simultaneously maximizes EMC robustness.
2.4 Timing Specifications
The SPI Timing is described in detail in chapter 5.2 (SPI Timing) in the Appendix.
T_tot_cycle Total Measurement Cycle Time = Data Cycle Time 900 1000 1100 µs
T_sgl_cycle Single Measurement Cycle Time 800 900 1000 µs
T_rd_out Readout Time - - 100 µs
Table 2: SPI Readout Timing
For a description of the above used expressions refer to chapter 5.2 (SPI Timing) in the Appendix.
SPOT CDS500D & CDS550D OEM Sensor SPI-Interface Specification_V1.1 Page 4 of 14
Christian Berg, T based on Felix Mullis, TL Created 11/10/2014 2:36:00 PM
Research & Development
Signal
Description
MIN TYP MAX
UNIT
2.5 Interface Hardware Specifications
2.5.1 Power Supply
Vcc Supply voltage 4.75 5.0 5.25 VDC
Ripple Supply voltage ripple and noise (BW = 20MHz) 50 mVpk-pk
Icc Supply current 1 5 mA
2.5.2 Recommended operating conditions
The input lines “Clk”, “SS/” and “MOSI” and the output line “MISO” are buffered with a SN74ABT125.
The output line “RDY/” is driven by a SN74AHCT1G125
SPOT CDS500D & CDS550D OEM Sensor SPI-Interface Specification_V1.1 Page 5 of 14
Christian Berg, T based on Felix Mullis, TL Created 11/10/2014 2:36:00 PM