Verrry nice Stu, thank you, having both units obviously does have its advantages after all:-) Pin 3 certainly controls the standby indication on the Z3811A and it's comforting to know it is indeed a solid ground during normal operation. However, given the low logic level seen on pin 2 I'm back to thinking it might be preferable to fit a pull down resistor to pin 2 when enabling stand alone mode rather than a direct short. A couple of quick measurements shows 0.223V across a 470ohm pull down and 0.446V across 1Kohm, the supposed indicated precision no doubt a fluke:-) but at least indicating a consistent current to ground of approx 0.5mA. So without knowing what's driving pin 2 I'm going back to a 470ohm pull down just to be on the safe side. Regards Nigel GM8PZR In a message dated 04/11/2014 09:38:25 GMT Standard Time, stewart.c...@gmail.com writes:
A wiring diagram of the Z3809A cable interconnect cable was published earlier on this list. That information appears to be incorrect. The cable is actually wired pin 1 to pin 15, pin 2 to pin 14, etc. Another way to describe it is that for each wire in the cable, the pin numbers on each end of the cable add up to 16. A mated pair of these units is running in my lab with a scratch-built interconnect cable following the above rules. This scratch-built cable allowed access to the interconnect signals while the system was operating happily. No lights were lit except the green ON light on the Ref-0 unit (Z3812A, no GPS) and the yellow STBY light on the Ref-1 unit (Z3911A with GPS receiver). The following signals were observed on the interconnect (pin numbers given for the J5 interconnect socket on the Ref-1 unit): Pin 1: 9600 baud serial data (described below) Pin 2: logic low (0.11V) Pin 3: Ground (0.00V) Presence detect? (see below) Pin 4: logic high (4.79V) Pin 5: inverted Motorola PPS, high (5V) for 800ms, low for 200ms Pin 6: "17 / 23 dBm" signal from Ref-0 unit (see below) Pin 7: logic high (4.48V) Pin 8: Ground (0.00V) Pin 9: logic low (0.11V) Pin 10: "17 / 23 dBm" signal from Ref-1 unit (see below) Pin 11: inverted PPS, low 400us, high (5V) otherwise Pin 12: logic low (0.12V) Pin 13: Ground (0.00V) Pin 14: logic low (0.08V) Pin 15: logic high (4.78V) Pins 3, 8, and 13 appear to be firmly connected to Ground. (Note that these are the three pins which are clipped short on the HP interconnect cable.) On an unpowered, disconnected box (either Ref-0 or Ref-1), pins 8 and 13 are connected to Ground (low resistance) and pin 3 is high impedance. Presumably pin 3 on each box (connected to the grounded pin 13 on the other box) is used to sense the presence of the other box and/or the interconnect cable. The timing of the PPS signal on pin 11 matches precisely the timing of the PPS signal available on pins 1 and 6 of J6 (RS422/PPS) on the active Ref-0 unit. Presumably this signal is coming across the cable from the Ref-0 unit. Note: when the system is coming up from a cold start, SatStat on the unit with the GPS receiver (Ref-1) will show "[Ext 1PPS valid]" in the space where it shows "[GPS 1PPS valid]" after the survey is complete. It appears that the Ref-1 unit timing system is locking its oscillator to the PPS coming from the Ref-0 unit during this time. The timing of the PPS signal on pin 5 matches the timing of the PPS output described in the Motorola OnCore manual. Presumably this signal is sourced by the Ref-1 unit to allow the Ref-0 unit to lock to GPS. The edges of this PPS signal look very dirty compared to the signal on pin 11. This may be an artifact of the homemade cable used for this experiment. The HP cable clearly has an overall shield (visible through the cable sheath) and may have internal coax or twisted pair for these PPS signals. When pin 5 and pin 11 are observed together, the usual GPS sawtooth pattern is evident. Someone discovered earlier that the both units will blink their green ON lights if the front-panel switch on either unit is set to 23 dBm vice the normal 17. Obviously each unit can communicate its switch status to the other unit. They use pins 6 and 10 to do that. Pin 10 (on the Ref-1 unit) is high (~5V) if the switch on the Ref-1 unit is in the 17 dBm position, and low in the 23 dBm position. Pin 6 (on the Ref-1 unit) gives the same indications for the switch on the Ref-0 unit. The serial data on pin 1 is transmitted at 9600 baud, with a burst of data every second. The signal idles at logic low (near 0V) and rises to logic high (near 5V) during the burst. This may be the standard for TTL (not RS-232) transmission of serial data, or it may be inverted. The first few characters of one burst were hand-decoded from a scope trace as 0x40, 0x40, 0x45, 0x61, 0x0B, or ASCII "@@Ea". This appears to be the Motorola Oncore binary data format, although "Ea" does not appear to be a valid Motorola command or response. Perhaps the hand-decoding was in error. One can use SatStat, talking to the Ref-0 (non-GPS) box, to issue queries and commands to the GPS receiver. The results are inconsistent, but it seems that at least some of the queries get through and trigger responses. If the Ref-0 box is actually talking to the GPS receiver, it must be doing so through the interconnect cable. The specific wire in the cable used for this (if any) has not yet been identified. An earlier post speculated that the computer in each unit only had two UARTs. This does not seem possible. Clearly each unit uses one UART to communicate with the J8 diagnostic port. The Ref-1 unit needs another UART to communicate with the GPS receiver. And both units need to be able to transmit the legacy Lucent timecode message out the J6 (RS422/1PPS) port. Perhaps there is a transmit-only UART coded into the FPGA, or perhaps one of the UARTs is timeshared with the Lucent message, or perhaps there is another UART chip hidden somewhere on the board. It seems unlikely that the two units are sending serial data to each other. (No such data was observed on the interconnect.) Instead, they appear to communicate their state to each other by means of logic levels on various pins of the cable. The logic functions of pins 6 and 10 have already been identified. Further research is needed. Cheers! --Stu _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
