11/09/2019 at 07:35 •
A DPST relay can be emulated with two SPST relays, with their coils in series (one coil replaces the pull-up resistor so energy efficiency is increased). However there are two problems :
- the high-side relay gives an inverted value
- the power-up value of the complementary latch gives a non-complementary value, both relays are left open.
The first problem is somehow "easy" to solve with the YGREC8 : the inverted value will go to SND because there is a XOR/inverter in the datapath. We just need to invert "in the other case".
The 2nd problem is solved by a diode, connected to a common /RESET rail that is momentarily connected to 0V during the power-up sequence. This means more diodes, but the power-up sequence can be shorter than some code scanning the register set and writing to each of them...
I just tested my system with the RES64 and it works well. The only problem is the capacitance of the RS flip-flop, the 47µF capacitor I tried is too large and 5µF would be good (a discharge time of 10ms) though I can't find the appropriate part.
The discharge time will determine the max. switching frequency (?), I think 10µF would still take a full clock cycle to discharge at 50Hz, and nothing prevents us from aborting the discharge. So I ordered more Russian 10µF tantalum caps.
This is also interesting because the much higher resistance of the RES64 coils keeps us from having to use large capacitors for timing purposes. For example, the POR (Power-On-Reset) could be controlled by a large capacitor (1000µF ?) discharging in a coil...
Experiments have shown very interesting results... Such as a 100µF capacitor with an internal 6K Ohms resistance ???
Because of this leakage current, the sensitive timing relay was still partially energised and wouldn't turn off after the RC time... Check your parts before using them !!!
No trick, I swear !
I make a 2-relays POR circuit now... Here is the schematic :
I botched the manual reset, is should be a SPDT switch so the 470µ capacitor is discharged fast (through 200 ohms or so).
The output has a weak pull-up resistor to backwards-bias all the diodes and (hopefully) reduce the crosstalk between all the latches.
3 more diodes help with discharging the capacitor or to prevent reverse-charging.
The 470µF cap provides a good 1s pulse.
The output RES64 could be buffered with more and stronger relays (like 3×RES15)
The only problem is with the voltage trigger : this voltage changes with time and self-heat... I'll have to find another system.
Oh and the trigger voltage varies with the ramp-up speed...
But this system is still more reliable than nothing. And I can select how many Ge diodes are in series to tune the voltage.
Another challenge : how do I detect that the voltage has dropped below 5.5V ?
11/05/2019 at 21:24 •
With the new RES-64 reed relays, the intended circuit must be adapted. Then with the experience gained with the other circuits, I came up with a different system that has several significant advantages over the prototype I made 2 years ago... But there is one drawback : it takes MORE RES-64 and more room !
The write section doesn't change : each bitplane requires a MUX8 to steer the bit to the appropriate coil, plus the latching relay+capacitor, that's already 8×RES15 and 8×RES64.
Reading however is different ! I simply took the large MUXes away, and I decode 3->8 with bipolar signals to select a whole register. I must add one diode per relay to prevent feedback loops but they are pretty small and cheap.
However there are 2 read ports and each latch must be duplicated because the RES64 are not DPST... that means a total of 144 RES64 !
Nothing crazy here, it's simply that I moved the MUX8 from the last to the first side, so it can be shared among the 8 bitplanes, which saves a significant number of relays.
Fewer relays make the system more dependable/reliable. The "sense buffer" (the same RES64 as the latches) needs less than 3mA and the MUX switches less than 3×8=24mA, the contacts are safe.
Of course it's not so simple : so many switches in parallel make feedback loops so we need diodes, one per switch, or 8 per bitplane, or 64 overall... But they are small and cheap so it's tolerable.
with the diodes, it might even be possible to use a bipolar system to save some decoding relays (MUX4 instead of MUX8), though it might be tricky...
It is also possible to latch the read bit, in case we need a pipeline latch or timing isolator.
But each RES64 is only a single switch and we need 2 of them, so unless I find a DPST reed relay that is similar enough, there are few choices :
- use/find/buy MORE RES64, which will take a lot of room
- use/find/buy more SIP reed relays (such as the Chinese ones I have found) because they are small and still cheap, though they break the "all-Russian style"...
- find a dual-switches reed relay... => unlikely.
This problem is specific to the register set because it has two read ports.
I/O and other registers have only one port (usually) so we can still use this method, for example for the scratchpad area.
Anyway, the huge parallel MUX8s were big annoyances and I'm glad I reduced their quantity. But I find myself with more questions to solve...
Lacking a proper, cheap, well-behaved DPST relay is not a catastrophe in itself. We can build one from two SPST relays by replacing the resistor with another coil, as in the sketch below:
The system will be less "clacky" because reading one operand will switch far fewer contacts. Maybe it's for the best for our ears, but it's certainly better for the overall reliability : the fewer energised relays, the fewer power it draws, the fewer points of failure...
Furthermore : this diode-OR system could be useful to save a few relays here and there, because the SRI operand gets data from a MUX in the datapath. The "read enable" can be disabled if an immediate value (or anything else) is required by the instruction.
10/25/2019 at 20:44 •
In the Y8, instructions come :
- from the program memory / PROM
- from the assembly panel
- from eventual "modern" sources
Then the instruction bits are amplified, eventually latched, and sent to :
- the processor's instruction decoder
- the disassembly panel
- eventually something else such as a semiconductor device...
This is a bit more complex than just plugging things together because all the electrical signals must be at the proper levels...
For now I have built the assembler panel and I start building the disassembler, and I'd love to test them together, but the levels are not compatible :
- The input is a low-current (2mA), medium voltage (about 6V) signal
- The output must be able to drive a string of RES15 coils (50 to 60mA max)
The RES64A is appropriate to buffer the signals and even latch them, if appropriate biasing is enabled.
The latch feature can be enabled on demand, for example during sensitive phases of the instruction cycle.
Another row of relays can also (dis)connect the RES64's coil from the input, to freeze the state of the processor while the memory and other circuits are in transient phases. The RES60 would be appropriate because it's small and DPDT so only 8 relays are needed, which uses much less room than the other methods. The 16× RES64 will use quite a lot of room, in comparison...
For convenience the latch doesn't use an intermediary capacitor because some operations require a direct connection to the core.
Now I have to find a PCB that can host 16× RES64...
20191118: I drop the idea of the RES60 latches because there must be a proper "instruction register". Program memory can also contain data that must be read by LDCL/LDCH and an early latch would make it harder later...
It also saves some of these precious relays.
So I started building the hub board on a smaller board, with only 3 connectors and their 48 diodes. More diodes provide the latching for the RES64. The relays will not be placed yet because I need to bin/sort the whole lot and I have not received everything yet. The preliminary data is in the log First plots.
The relays will be placed on staggered positions on both sides of the board to save space, just like it will be for the register set.
Hopefully I'll have some room left in the corners for mounting holes...
10/25/2019 at 03:02 •
I received 72× RES64A from Moldova and I'm pretty happy and lucky :-)
@Artem Kashkanov praised the RES55 he uses : the lower current and the higher hysteresis compared to RES15 would be great and I was eager to test something.
The log 86. Sensing relays explored the question of the reed relays and found that even cheap 12V relays from China have desired features for certain circuits of the YGREC8 : mainly as sensors/amplifiers because they require much less current for activation.
I just measured a RES64A and the reference I received is pretty awesome !
- Von : 4.3V
- Ion : 2.1mA
- Voff : 1.7V
The case is pretty bulky but this adds to the charm. With a suitable price, I'd get more of them and use the high hysteresis to build the register set as well.
Even at 2.5mA (worst case), the gain is really significant ! It is less than 1/10 the current required by the RES15 and the hysteresis is somewhat higher, which means : much more stability ! And no need to bin the parts !
Total current : 2.5 × 8 × 8 = 160mA max !
This considerably relaxes the constraints on the power supply, the ripple (and filtering capacitance) is much less and the whole is less sensitive to interferences...
However the supply voltage would be 4.3 + 1.7V = 6V and I'll have to find/design the proper power supply and transformer... But 6 × 0.16 = 1W max !
Now I have to find enough vintage Russian 2K resistors...
There is another change : the RES64 is SPST so it's only on or off... the RES15 is SPDT and can switch the output from +Vcc to -Vcc so it's pretty convenient for the output levels. A register set made of RES64 will require some sort of buffer (maybe another RES64 per bit, so I'll need 72 of them)
10/24/2019 at 23:41 •
This other module is now OK as well !
What a mess... There were a number of blunders but I managed to find and correct them all.
The component side is nice but the wire side is ... less nice.
I somehow managed to swap and invert some signals so it is not an exact copy of the schematics (shown below again for reference)
This circuit decodes 3 input bits to the following symbols on 7 segments :
A 4th bit is inverted with a relay to drive a small Glühbirnchen and signal inversion. Maybe I should also output the "NEVER" condition on the last signal of the connector...
The system is shown and operated in this short video :
I hope you enjoy hearing the relays' clicks :-)
I also added an auxiliary output to help signal the "NEVER" condition.
However the polarity is inverse (compared to the hexadecimal modules) and can't be displayed on the usual test module.
A reversed diode and a Glühbirnchen are enough but I'll see later how to better exploit this signal (in conjunction with the 4th "neg" bit).
10/24/2019 at 17:45 •
Hi dear reader ;-)
Some pictures would probably please your eyes, I hope you enjoy the sight !
It was quite some work but the result is nice. The only gotcha was a forgotten diode/segment in the decoder at NU2.A:
Here is a video of one unit under test :
I reuse the same pinout and test board as the #Numitron Hexadecimal display module for convenience :-)
I'll have to do some "optical design" to prevent glare/reflections and keep the Numitrons readable, but this is for another time. As you see, I use a separate connector for modularity so I can design the front panel independently.
I'm already working on the condition display...
10/16/2019 at 02:06 •
In the log Don't go full Numitron ! Unless... OK whatever. I examine how to reuse the techniques developed in #Numitron Hexadecimal display module and apply them to decode all the fields of the Y8 instruction.
For the register name I came up with this diagram :
This decodes to the following symbols :
The segments E1 and G1 are always on (for A, d, r and P) so I modified the diagram a bit, later.
I didn't optimise the replicated 1 and 2 because it would make the relay side too complex for little gain (I only have to build 2 decoders). Here is the result :
To test the circuit, I have built a test device with a "standardised" 26-pins connector and 3 Numitrons. To inject data, I will reuse the connector and pinout of the existing Numitron hexadecimal modules.
Note : the module can be powered down by disconnecting the +3.3V power line. The diodes will prevent shadow segments anyway, even if another decoder is connected in parallel to the Numitron (for example to share the Imm4 and Reg formats).
10/15/2019 at 00:28 •
The RES15 relay is nice but requires way too much current to operate, in particular in some circuits where low current is necessary : the DRAM sense circuit as well as the instruction sense circuit, because 16 bits multiply the coil current, that reaches a value that can't be reliable...
Another type of relay is required and @Artem Kashkanov suggested the RES55 : a reed-type relay with the typical fast operation and low operating current, though at a higher voltage.
I couldn't find a suitable lot of this reference on eBay but found 2 other things :
- RES-64A rated 9-11V : vintage, pretty bulky, only SPST but 2K ohm coil so it must be pretty sensitive
- 1A12 : miniature SIP chinese reed SPST relays, rated 12V, 1K ohm coil, very cheap
I just tested the 1A12 and I am impressed : the contact closes at about 5V (varies with the piece) and opens at about 3V, with a current under 2mA. With such a hysteresis and low power, it even becomes interesting to use them for the register set...
I still have to receive the RES-64A, which would look way better, and I'll have to compare it to the modern miniature version. However there is now a good solution to the problem I had before : I can switch 16 bits on, and draw at most 2×16=32mA, which will not strain the address decoder's contacts much.
Oh and I still have to design that automated relay tester...
10/12/2019 at 23:23 •
I made it !
I had to correct a couple of blunders (see the diagram below) and now the system woks (almost) as expected !
Not all the forbidden/impossible codes are prevented :
- IN and OUT seem to allow the IMM4 and REG modes, though the output binary code will be decoded "correctly"
- INV allows SND to be output
- probably some other obscure combinations are possible
However this panel is only one half of the ASM equation : the disassembler display will prevail over the buttons configuration.
This is why some markings are missing : when programming, look at the output and trust the display, don't stare at the buttons.
(I'll have to shoot a video...)
10/06/2019 at 15:07 •
It took a long while, efforts, expenses, and a full disassembly of my laser printer but here it is !
The look/aspect is great ! I had some little issues with the size (maybe due to slight resizing somewhere) and there are a few hicups with some mounting screws.
However the toner ink sticks rather well to the vinyl sheet and glueing didn't leave bubbles. The alu face plate can remain (mostly) clean and it adds a lot to the ergonomics :-D
Locating the "right" plastic sheet took a while...
And here it is in all its glory !
All the switches are soldered but the assembly/wiring is not complete, I need to add another board to really get all the signals together. So I created a small board with 16 Glühbirnchen to ease the tests :-)