Dr.J

Thank you @zygot — that's extremely helpful. For multiple ADC boards we are implementing an external power supply on the ZMOD board that will supply the current we need, but we also need a compact setup that will draw its power entirely from the ZMOD. The aim is to keep the current draw below that available from the USB104 when powered over USB so that entire chain is power from whatever DAQ device we use to power the USB104. On a related note, it looks like there are limitations on which pins we can choose on the ZMOD connector to adhere to the SYZYGY specification: particularly that pins need to be utilised sequentially. If we have 5 signals as LVDS pairs and 3 single-ended, I'm assuming that means our differential pairs must be on pins 5 to 15 and then pins 14, 16 and 17 have to be utilised for the single-ended signals. Since 3 of the LVDS pairs are clock signals, is it necessary for the USB104 to use the specific Carrier-to-Pod differential pair (pins 34+36) for these? This would mean skipping out some 20 pins which goes against the SYZYGY spec. Also, is the SYZYGY EEPROM needed in order for the USB104 to communicate with a ZMOD daughterboard? According to the SYZYGY spec an EEPROM is needed to store some configuration data, including the current and voltage requirements of the ZMOD daughterboard. What happens on the USB104 if this isn't present? If its essential, is it possible to programme this EEPROM as part of the USB104 start-up cycle or when the ZMOD daughterboard is connected, or does it have to be programmed prior to connection?

Hi @JColvin, Thanks for clarifying. I think I was getting the 3.0Amps current from misreading Table 1.2.1. I have another question regarding LVDS signalling from the USB104. We need to design a ZMOD daughterboard to interface with some analogue electronics that is built around a Texas Instruments DDC232 chip. We are sending 5 of our more time-critical clock signals as differential pairs and the remaining 3 as single-ended. We would like to send the differential pairs as LVDS pairs since that's what our analogue electronics is currently set up for. What is the maximum voltage we can use for LVDS pairs on the USB104 through the ZMOD port to a SYZYGY daughterboard? 3.3V, 2.5V or 1.8V? If its not 3.3V, can we use 3.3V for the single-ended signals? Also, would the only way to supply more than 1.5A to this ZMOD board be to attach another external power supply? It sounds like there is no way of passing more than 1.5A at 5V from what you are saying. Our analogue boards are rather power hungry...

Hi @JColvin, If the VIO supply current is limited to 1.2A, what about the 5V supply current? Will that provide the 1.5A in the SYZYGY specification? Given that one can use an external power supply up to 6A does this mean more current is available to the ZMOD connector? I'm a little confused about the VCC5V0 current values given in the power specifications table 1.2 in the USB104 reference manual which seems to suggest as much as 3A is available on the 5V rail. The more current we can supply through the ZMOD connection the better.

Hi @JColvin, That's really useful: thank you. I'm particularly glad we can get 5V from the ZMOD port. If you look at the specifications from the URL I linked to above, under "Electrical", it says: SYZYGY Connectors: 1.2V to 3.3V, up to 1.2A depending on power source. Automatically negotiated on board bring-up So that's where I was getting the 3.3V and 1.2A limits from. If I understand you correctly, this is for the various VIO ports, not the supply rail. We don't need to drive high currents over the VIO ports but may need more than 1A on the 5V supply rail.

What is the maximum voltage that can be supplied from the ZMOD port on a USB104? The documentation says that the USB104 conforms to the SYZYGY standard, which means both 3.3V and 5V should be available. However, on the Diligent USB104 reference page it says 1.2V to 3.3V: https://digilent.com/reference/programmable-logic/usb104a7/start ...which would mean it differs from the SYZYGY spec. Does this 3.3V just refer to the various signal pins or also to the 5V supply rail? Also, if the 5V is supplied, does this provide up to 1.2A as specified? We have an analogue board we need to power that could be quite power hungry.