Hello! I am having a problem using another microcontroller to control the ADE-7880 via SPI using the ADE-7880 EVK through the isocoupler. I have an isolated power supply (using a 3-prong to 2-prong AC adapter plug) providing 3.3V on connector P9, the USB plug is connected to a laptop to provide power to the NXP LPC2368 domain, and I have JP21 firmly seated across 1 and 2. I have pressed the reset button S2.
As you can see from the following oscilloscope capture (the oscilloscope is also isolated using another 3-prong to 2-prong AC adapter plug), I am providing SS and SCLK signal to P17-3 (SCK, channel 2 in light blue) and P17-5 (SS, channel 3 in magenta purple):
However, when I measure at the test points “SCLK_ISO” and “SSD_ISO”, it appears the signals are still getting mashed by the NXP LPC 2368:
Also, if I switch the oscilloscope ground (it is currently connected to P17-2) to a ground on the domain of the ADE-7880 and measure at the test points “SCLK/SCL” and “SS/HSA”, it is just a solid high (3.3V) signal.
In the user guide (UG-356), on page 9, in the section titled “Using the Evaluation Board with Another Microcontroller”, it says “if P17 is used, a conflict may arise with the NXP LPC2368 I/O ports. To avoid this conflict, close the JP21 jumper. This tells the NXP LPC2368 to set all of it’s I/O ports high to allow the other microcontroller to communicate with the ADE-7880.” But shouldn’t closing JP21 tell the NXP LPC2368 to set all of it’s I/O ports open/floating? How else can an external microcontroller drive the SPI signals? Should I try something like put a 1K in series with the SPI control lines or will this cause damage?
