Connect Shield Documentation Questions | Telit Cinterion IoT Developer Community
October 2, 2019 - 6:24pm, 2708 views
Hi, I've been using a Cinterion Connect Shield with ELS61 in standalone mode (USB to my laptop). Able to connect, ping, etc. Now I want to connect the Shield as a peripheral to my Nordic nRF52840-DK board. I downloaded and reviewed the documentation for both boards to make sure I power the Shield correctly and connect the Rx and Tx lines correctly. The Shield document from the Gemalto website is "connect_shield_ug_v02.pdf".
1. Table 1 on page 9 shows that Arduino TX is connected to Modem RxD0, and Arduino RX is connected to Modem TxD0. But the Shield schematic on pages 16 and 17 shows that Arduino TX is connected to Modem TXD0 (via TX_5V and TXD0_1V8), and Arduino RX is connected to Modem RXD0 (via RX_5V and RXD0_1V8). In other words, the table says they're swapped but the schematic says they're straight through. Which is correct ?
2. I'm having trouble understanding the relationship between the 5V and 3.3V supply inputs and the IOREF input. Does the Shield require both 5V and 3.3V power, or will 5V alone be adequate ? If it does require 3.3V, will 3.0V be adequate (the Nordic DK supplies 3.0V, not 3.3V). And am I supposed to tie IOREF to one of the supply inputs ?
1. RS232 interface on the module is using 1.8V logic while on Arduino connector there 5V.
According to the schematic RXD0 line of the module is connected to RXD0_1V8 which is connected to Arduino connector (RX_5V line) via the level shifter.
In 'Figure 2: Connect Shield’s Arduino UNO interface lines' there's also RXD to RX mapping. So for now I don't know why it is the opposite way in Table 1 and I don't have this hardware at the moment to check. But this layout is standard - Arduino has the same description and is using TX as output and RX as input. This corresponds to the DCE-DTE convention used by the module - the module (DCE) communicates with the customer aplication (DTE - in this case it would be Arduino board) as follows:
- TXD line of customer application sends data to the module’s TXD0 signal line
- RXD line of customer application receives data from the module’s RXD0 signal line
So on the module TXD is an input and RXD is an output.
2. According to the document 3.3V input is needed for powering I2C sensor only. So if you don't want to use the sensors on the board it may not be necessary. IOREF is not connected according to Figure 2 and Table 1.
Hi Bartłomiej, thanks very much for your explanation. All clear now.
Hi again Bartłomiej,
Well I thought it was all clear - at least the DTE/DCE stuff is clear now.
Another related question - the board contains an ELS61-US module. The board schematic says that RXD0_1V8 and TXD0_1V8 connect to pins 11 and 13 of the module (they both show "*2" next to the pin numbers, which normally means see note #2, but there are no notes explaining the asterisk anywhere, so I have no idea what "*2" means). I also have the ELS61-US Hardware Interface Description (els61-us_hd_v02002.pdf), and it says that RXD0 and TXD0 are pad numbers 210 and 212, not 11 and 13. A quick check of a few other pins shows that the schematic and HID generally agree (e.g pin 33 is EMERG_RST in both places).
I'm transmitting data from my PC to the board and probing around with an oscilloscope. I can see the transmitted data at TX_5V on IC13 pin 4. I can see it at TXD0_1V8 on IC13 pin 3. But I can't see it at the ELS61-US module, either on pins 11 or 13 (if you assume that the pin numbering starts at 1) or on pins 210 or 212 (if you assume that the pin numbering starts at 201 as shown in the HID).
Can you figure out where RXD0_1V8 and TXD0_1V8 actually go on the board ?
Update - I went around the pins of the ELS61 with a scope probe until I found TXD0_1V8. Powered off and checked it with an ohm meter. Cross-referenced with ELS61 HID pages 15 and 16:
TXD0_1V8 / IC13.3 - tied to ELS61 pin 57 (schematic says pin 13 *2) - HID calls this GND
RXD0_1V8 / IC11.3 - tied to ELS61 pin 59 (schematic says pin 11 *2) - HID calls this ANT_MAIN
I'm thoroughly confused now. Thanks
I haven't heard of such a mistakes (with pin numbers) in harddware description document so far. Both 57 & 59 and 210 & 212 pin pairs are on the module's edge. Are you sure that you have identified the correct edge? The figure shows the module's bottom view.
Yes you were right, I was looking at it from the top so mirror imaged. The pinouts listed are indeed correct.
Now, another question about the Connect schematic that's included in "connect_shield_ug_v02.pdf": Pages 16 and 17 of the UG are pages 1 and 2 of the schematic, but the schematic indicates that there are actually 3 pages. i.e. the 2 pages are labeled Sheet 1/3 and Sheet 2/3. Also, the RXD1 and TXD1 pins of the modem are connected to "RXD1/" and "TXD1/" respectively, seeming to reference the 3rd page.
Would you know where I can find the missing 3rd page of the schematic ? Maybe there's a later version of the PDF ?
I'm sorry that it took so long. In fact ASC1 (you have mentioned RXD1 and TXD1 pins) is not connected to any external interface of the board. I've got some information about the missing page for you. The page 3 is not published in any version of Connect Shield User Guide as it does not contain any useful information. There's only some small circuit connected to ASC1 which is not present on the real Connect Shield board. So this page could be causing some confusions if added to the document. I don't have this 3rd page yet but I may get it next week.