Emax

Yes, an oscilloscope is what you need. I suggest getting a digital model as it should allow you to capture and store the signals you are measuring. Some 
high end multimeters also have oscilloscope functions, but check the bandwidth is well above the highest frequencies you will need to measure. An audio 
card is not suitable for this task.

I did a search on the Mac serial port and it seems that while the output voltage levels are slightly non standard they should not present any problems for 
the Emax 9637 RS422 receiver chip. I only have the Emax II schematics but I believe the RS422 interface should be the same as the Emax. The 9637 
circuit doesn't appear to have any EMI supression or termination other than a pullup to +5V on the noninverting input. So the Emax is relying on the 
sending circuit to ensure a reasonably clean signal arrives. The Mac has an EMI filter on its RS422 port but I am not sure what your PC RS422 port may 
have.

Another thing to look at is the relationship between the 500kHz clock the Emax sends out and the data that is sent back to the Emax from the PC. The 
6850 UART in the Emax relies on a this being within a certain timing range. If the clock to data relationship from the PC RS422 port is not the same as 
from the Mac then this could cause problems. The same would also occur if the PC RS422 transmit clock is drifting because is not locked to the same 
clock that it is receiving from the Emax. Of course the data being sent from the Emax to the PC will be ok because the clock and data are transmitted 
together with the correct timing relationship.

/Tristan

Tuesday, November 18, 2008, 3:58:48 AM, you wrote:

>
To have 100% certainty about the actual problem I should indeed do 
some measurements with an oscilloscope... but I don't have one.
I was (and still) am thinking about buying one, either analog or 
digital. Until now I only did some measurements with an external 
audio card acting as a wave recorder, but its sampling frequency and 
bandwith are - of course - insufficient to do proper measurements on 
500kbaud signals. What I do see however - even with this method - is 
that the amplitude level of the Mac signal is much higher than the PC 
signal.
On the other hand, if the RS422 of the Emax is standard, then I 
shouldn't have any problem. Mmmm... 
Yes, the best solution would consist of a custom RS422 port for the 
PC which can even be externally clocked. But I'm not an electronics 
specialist so it will take a looooonnnnng time before I will end up 
with a working set :-)

///E-Synthesist

--- In emax@yahoogroups.com, tu@... wrote:
>
> I am not sure about the Mac circuitry but the RS422 interface on 
the Emax should just be standard 
> 9637 and 9638 RS422 buffers. The input threshold on the 9637 
receiver is specified to be +/- 
> 200mV so it should work with voltages higher than that. Do you have 
an oscilloscope that you can 
> use to probe the 9637 while it is receiving data? If so, you could 
compare when receiving data 
> from the Mac and the PC via RS422.
> 
> Its not a priority, but I think it would be worthwhile to have an 
RS422 interface that would allow 
> any PC to be used for sample dumping to the Emax I, Emax II, EII, 
EIII and EIIIx as well as bank 
> transfer with the EII and Emax. Even if an interface box cost some 
money I feel there would be a 
> demand given the numbers of these samplers still in use. The Emu 
world cannot live on old Macs 
> alone :)
> 
> /Tristan
> 
> Monday, November 17, 2008, 3:24:57 AM, you wrote:
> 
> >
> After some additional testing I'm pretty sure the problems are not 
> caused by timing differences, but by voltage levels. 
> I received a PCMCIA RS422 port this week, and this thing has even 
> more problems with communicating with the EII and the Emax than my 
> USB/RS422 converter device. And again the communication problem is 
to 
> be found in the PC->Emax transmit part, not in the receive part.
> I mentioned before that the Mac RS422 is sending very high signal 
> levels (higher than "officially" allowed by the RS422 standard). 
The 
> Emu samplers seem to rely on these high signals.
> Conclusion: I give up the current experiments. Perhaps some time in 
> the future I'll try to make a device based on Mac circuits...
> 
> --- In emax@yahoogroups.com, tu@ wrote:
> >
> > Ok, that is interesting.
> > 
> > An alternative to direct connection of the RS422 to the PC would 
be 
> a microcontroller sitting 
> > between the PC and sampler. I think someone suggested that 
before. 
> It could respond to the 
> > sampler with tight timing but handle the loose timing over the PC 
> connection. I guess the PC side 
> > could be implemented with either RS-232 or USB. But obviously USB 
> would require a lot more 
> > coding than simply translating RS422 and RS232 port protocols 
with 
> a bit of buffering in between.
> > 
> > /Tristan
> > 
> > Wednesday, November 12, 2008, 1:15:37 AM, you wrote:
> > 
> > >
> > Yes it's about the same concept as on the EII: taking an exact 
dump 
> > of the internal Emax memory at 500 kbaud in both directions. Or 
in 
> > other words... transferring an EMX file across the serial line 
> > (except for the EMX 39 byte header string of course).
> > 
> > But there are two major drawbacks compared with the EII: 
> > 1/ the Emax uses the MMA standard to accomplish this dump, 
meaning 
> > that the data is sent in packets of 120 bytes instead of 256 
bytes, 
> > which is slower.
> > 2/ it's not possible to dump specific memory segments, the whole 
> > thing must be dumped in one sequential loop from the very 
beginning 
> > (position 0) to the very end (position 552959). 
> > 
> > The second one is a BIG problem: it means that if something goes 
> > wrong (like a bad packet) the whole dump must be restarted.
> > And... since the PC RS422 communication line with the Emax is not 
> > optimal, this kind of error will for sure occur during a bank 
> > transfer. On the EII, this means simply re-asking for the 
> particular 
> > bad data packet, but on the Emax you have to start all over again.
> > 
> > In practice this means that a full load/unload is simply not 
> possible 
> > with my current hardware (USB-RS422 and USB-RS232 converters of 
all 
> > kinds) because the loop is restarted endlessly. At the end of the 
> > week I'll try an non-USB port device, I hope that one will work.
> > If not, a custom RS422 PC port must be built for the Emax/EII, 
> based 
> > on the RS422 circuits & ICs of the Mac.
> > 
> > ///E-Synthesist
> > 
> > --- In emax@yahoogroups.com, tu@ wrote:
> > >
> > > Fantastic! So, is it the same method that the EII uses for bank 
> > transfer or something else? Is there 
> > > any chance you could document the protocol? 
> > > 
> > > I think 25-30 seconds should be acceptable for Emax I bank 
loads. 
> > At least it provides an option 
> > > for those who can't or don't want to add SCSI. 
> > > 
> > > The Emax II load time does sound a bit slow. But it might still 
> be 
> > of use if someone had a working 
> > > Emax II with a dead SCSI chip.
> > > 
> > > Out of interest, can the Emax II directly load an Emax I bank 
> (with 
> > compressed 8 bit samples) in 
> > > this way? 
> > > 
> > > /Tristan
> > > 
> > > Tuesday, November 11, 2008, 3:04:25 AM, you wrote:
> > > 
> > > >
> > > After some experiments during the weekend, the current status 
of 
> my 
> > > little RS422 project is that I know how to do *fast* bank 
> > > loads/unloads on the Emax via RS422. 
> > > This should reduce the total data transfer time to 25-30 
seconds 
> on 
> > > the Emax-I instead of the 2-3 minutes of Alchemy. Most probably 
> > this 
> > > was also the total load time of the OMI CDS3 system, which is - 
> > let's 
> > > say - "acceptable"... 
> > > That's about the same speed as loading from a floppy :-) but 
the 
> > > biggest advantage would be that one would have immediate access 
> to 
> > > hundreds of banks on the PC harddrive instead of having to copy 
> > > individual banks to floppy disks first... 
> > > Still SCSI is a much better alternative... for those having a 
> rev2 
> > or 
> > > rev3 board, and for those using the Emax-II. BTW at RS422 
speed, 
> > the 
> > > data transfer time on a fully loaded Emax-II Turbo 8M would be 
> > about 
> > > 7 minutes :-). Fortunately every Emax-II is equipped with SCSI.
> > > 
> > > I have to write some decent software now which supports the 
full 
> > Emax 
> > > handshaking protocol. But I'm pretty sure that the USB<-->RS422 
> > > converters will not be the best solution for this 
communication - 
> > > just like with the EII the communication seems to be quite 
> > unreliable 
> > > when transmitting data from the PC to the Emax, as a 
consequence 
> > the 
> > > total transfer time increases dramatically due to handshaking 
> > > overhead. 
> > > At the end of the week I will have a PCCard RS422 port on my 
> > laptop. 
> > > This piece of hardware does not suffer from USB latency, so I 
> hope 
> > it 
> > > will work better...
> > > 
> > > ///E-Synthesist
> > > 
> > > --- In emax@yahoogroups.com, "esynthesist" <esynthesist@> wrote:
> > > >
> > > > Yes, I was also thinking there must be some dedicated command 
> > (set) 
> > > > for fast load/unload. But the fact that John remembered a 
load 
> > time 
> > > > of 5 minutes for the OMI cdroms made me doubt again... On the 
> > other 
> > > > hand it is true that OMI cdroms could only be used after the 
> > > release 
> > > > of OS 3.2, so this is indeed an indication that additional 
> > commands 
> > > > have been added, or at least some changes have been applied. 
I 
> > also 
> > > > observed that the v 3.2 MIDI protocol is not 100% behaving as 
> > > > described in the v 3.0 document, e.g. the timeout handling is 
> > > > different. So there are also changes in the 'normal' 
SYSEX/MMA 
> > > > protocol.
> > > > By the way: the OMI drive also required a firmware update in 
> > order 
> > > to 
> > > > be compatible with the Emax. Question is of course whether 
this 
> > was 
> > > > just a small firmware update (to support the newly added 
> commands 
> > > in 
> > > > the Emax OS) or a huge piece of Emax-specific code (to 
> implement 
> > > the 
> > > > full SYSEX/MMA command set - which is indeed quite 
unlikely) ...
> > > > 
> > > > The Emax-II and EIII indeed have a filesystem which is 
> optimized 
> > > for 
> > > > handling different banksizes; I have the specs here because I 
> > > needed 
> > > > them for EMXP. The EII and Emax are using filesystems with 
> fixed 
> > > > filesizes in a sequential order.
> > > > 
> > > > Since I don't have any Emax OMI cdrom disk I'm not even sure 
> > > whether 
> > > > the banks on these disks are "EMX-like" 8-bit images or 
> expanded 
> > 12 
> > > > bit images. It makes sense that they are 8-bit, because this 
> > > allowed 
> > > > OMI to put more banks on a CD, to transfer them faster to the 
> > Emax 
> > > > (if EII-like commands have been implemented in the Emax OS of 
> > > course) 
> > > > and to use the same bank layout as on the Emax floppy and 
Emax 
> > > > harddisk banks.
> > > > 
> > > > So despite the "5 minutes load time" note from John, I think 
we 
> > can 
> > > > still assume that there is some specific command set in V3.2 
> > which 
> > > > enables fast bank loads. I will try to find them out during 
the 
> > > > weekend, either by experimenting or by looking into the OS 
> > > > binary/disassembled code...
> > > > 
> > > > ///E-Synthesist
> > > > 
> > > > 
> > > > 
> > > > --- In emax@yahoogroups.com, tu@ wrote:
> > > > >
> > > > > 
> > > > > Thursday, November 6, 2008, 4:23:43 AM, you wrote:
> > > > > 
> > > > > >
> > > > > But the 5 minutes load time may have been reality...
> > > > > 
> > > > > This can explain why I don't know anyone and find no 
> reference 
> > at 
> > > > all 
> > > > > of anyone who actually used this CD-ROM drive with the 
Emax. 
> If 
> > > > this 
> > > > > 5 minutes load time is true, this must have resulted in a 
> > > > commercial 
> > > > > failure for OMI when they launched the Emax OMI cd disks... 
> but 
> > > > they 
> > > > > probably released these disks also in Mac/SD format ?
> > > > > 
> > > > > 
> > > > > 
> > > > > 
> > > > > Yes, such a slow load time would have been a major 
marketing 
> > > > problem. I find it difficult to imagine that Emu would not 
have 
> > > added 
> > > > the small amount of 
> > > > > extra code required to load in a bank quickly via RS422. If 
> > they 
> > > > wanted to sell Emaxes then surely there was a strong 
incentive 
> to 
> > > > make the sound 
> > > > > library efficient to use. I suspect the OMI CDROM system 
for 
> > the 
> > > > Emax was not a major market success because of the cost. The 
> OMI 
> > > > CDROM drive, or 
> > > > > even a Mac with a CDROM drive, would have cost a 
significant 
> > > > proportion of the cost of an Emax. The average musician 
> probably 
> > > > would not have been 
> > > > > able to justify that additional expense. Particularly so 
> given 
> > > that 
> > > > early CDROM drives were rather fragile.
> > > > > 
> > > > > >
> > > > > 
> > > > > And yes, Emu has done strange things. E.g. the EII cdrom 
kit 
> > > > > supported a "folder" or "category" system: the banks on a 
> disk 
> > > > could 
> > > > > be put in folders (like bank "piano" in folder "acoustic 
> > > > keyboards") 
> > > > > to make navigation much easier. This feature was not 
> available 
> > on 
> > > > the 
> > > > > Emax and EIII harddisks. Maybe Emu considered this to be a 
> > > feature 
> > > > of 
> > > > > OMI and not of Emu themselves, but they could have learned 
> from 
> > > > > that...
> > > > > 
> > > > > 
> > > > > 
> > > > > 
> > > > > Surely the category organisation was only a feature of the 
> OMI 
> > > > CDROM system, as the EII had no control over it. So it was 
> OMI's 
> > > > CDROM format, not 
> > > > > Emu's format. But this also gave OMI the flexibility to put 
> as 
> > > many 
> > > > banks on the disk as they wanted and to organise them as they 
> > > wanted. 
> > > > There was 
> > > > > no restriction on how OMI could do this as long as they 
could 
> > > serve 
> > > > up the full memory image of each bank to the EII via the 
RS422 
> > port 
> > > > when required.
> > > > > 
> > > > > Don't the Emax and the EII hard disk formats allocate a 
fixed 
> > > > number of banks for the disk? I believe you cannot fit any 
more 
> > > banks 
> > > > on the disk even if 
> > > > > the existing banks are only half full of samples. 
Presumably 
> > this 
> > > > is because the Emax and EII use a fixed memory size for each 
> bank 
> > > and 
> > > > the complete 
> > > > > data for the bank is copied directly between memory and 
disk 
> > when 
> > > > you load or save a bank. Each hard disk bank is a the 
> equivalent 
> > of 
> > > > one floppy disk 
> > > > > image minus the OS data. I believe the Emax II and EIII use 
> > > > variable sized banks. Therefore the number of banks stored on 
a 
> > > hard 
> > > > disk or CDROM 
> > > > > depends on how much data is contained in each bank. But I 
> > believe 
> > > > there is still a limit of 100 banks per disk. 
> > > > > 
> > > > > >
> > > > > 
> > > > > 
> > > > > 
> > > > > RS422 Communication with the Emulator was designed based on 
> > > > following 
> > > > > key principles:
> > > > > - all communication, including request/reply for parameter 
> > > changes, 
> > > > > occurs at 500 Kbaud
> > > > > - a whole bank can be downloaded/loaded with one special 
> > designed 
> > > > > type of command (a command which actually directly 
> reads/writes 
> > > the 
> > > > > RAM memory segments in which the bank data is residing)
> > > > > - bulk data load/unload occurs with data packets sized 256 
> > bytes, 
> > > > of 
> > > > > which each byte represents 1 sample point (data is 
> transferred 
> > in 
> > > > > compressed format)
> > > > > 
> > > > > On the Emax, they seem to have decided that choosing for a 
> > > > *standard* 
> > > > > medium speed protocol was more important than choosing for 
a 
> > > > > *proprietary* high speed protocol. So they went for the 
MIDI 
> > > > > SYSES/MMA approach:
> > > > > - all basic communication, including all 
> commands/instructions, 
> > > > > occurs at 31.25 Kbaud, no matter if the DIN5 MIDI sockets 
or 
> > the 
> > > > DB9 
> > > > > RS422 port are being used.
> > > > > - loading/unloading banks requires the full set of SYSEX 
> > > commands. 
> > > > > Hence to simply download the parameters of just one voice 
of 
> > just 
> > > > one 
> > > > > preset, already multiple commands must be exchanged with 
the 
> > > Emax. 
> > > > > This is due to the fact that in general only one parameter 
> can 
> > be 
> > > > > transferred per command. And this must be done at the slow 
> > 31.25 
> > > > > Kbaud speed...mmmm...
> > > > > - bulk data (sample) load/unload occurs with data packets 
> sized 
> > > > only 
> > > > > 120 bytes (MMA standard). Moreover each sample point 
requires 
> > 12 
> > > > bits 
> > > > > now instead of 8 bits on the EII since data is transferred 
in 
> > > > linear 
> > > > > format instead of compressed format.
> > > > > As a consequence, loading/unloading banks is much slower 
than 
> > on 
> > > > the 
> > > > > EII. Of course, once they released the Emax-II, they would 
> have 
> > > > faced 
> > > > > problems anyway. This machine could have up to 8MB banks 
and 
> > > > doesn't 
> > > > > use compression, so even at full 500 kbaud speed and using 
> only 
> > > one 
> > > > > command - which is impossible in reality - the Emax-II 
would 
> > > > require 
> > > > > at least 2.7 minutes for loading/unloading banks. 
Fortunately 
> > > there 
> > > > > was something invented called SCSI :-)
> > > > > 
> > > > > 
> > > > > 
> > > > > 
> > > > > Have a look at the MIDI spec for the Emax V3.0 software. 
The 
> > fast 
> > > > (RS422) dumps use a protocol based on the MIDI SDS but 
slightly 
> > > > modified. The 
> > > > > sample data is dumped as 12 bit linear but the samples are 
> > packed 
> > > > so that two 12 bit samples are transferred in three 8 bit 
> bytes. 
> > It 
> > > > is also of note that 
> > > > > sending 8 bit wide data in this way violates the MIDI 
> standard, 
> > > as 
> > > > bit7 is always reserved as an indicator of a status byte. Of 
> > course 
> > > > this is not really an 
> > > > > issue here as the 500k baud RS422 data is only being 
> > transferred 
> > > > to/from the Emax so no other MIDI devices will ever see this 
> > > > violation of the 
> > > > > standard. But the outcome is that dumping samples as 12 bit 
> > only 
> > > > takes 50% longer than dumping as 8 bit compressed. Doing a 
> proper 
> > > > MIDI SDS dump 
> > > > > of 8 bit or 12 bit data actually takes the same amount of 
> time 
> > as 
> > > > only 7 data bits can be transferred for each byte in the 
> message. 
> > > So 
> > > > an 8 bit dump 
> > > > > takes two bytes per sample (7 + 1) while a 12 bit dump also 
> > > > requires two bytes per sample (7 + 5). 16 bit dumps are even 
> > slower 
> > > > as they require three 
> > > > > bytes per sample (7 + 7 + 2).
> > > > > 
> > > > > As you have said, the failure to provide a means of 
directly 
> > > > transferring banks into memory via RS422 seems to be the 
> problem 
> > in 
> > > > the Emax, at least as 
> > > > > documented in the V3.0 MIDI spec. But if the V3.0 spec 
> already 
> > > > provides all the functions required to load banks from the 
> CDROM 
> > > > drive using MIDI 
> > > > > SYSEX and RS422, then why is V3.2 or the SE software 
claimed 
> to 
> > > add 
> > > > OMI CDROM support? It still seems likely to me that some 
extra 
> > > > functions were 
> > > > > added in those versions to support fast bank loading via 
> RS422. 
> > > If 
> > > > not, then the OMI CDROM drive would have to be converting the 
8 
> > bit 
> > > > compressed 
> > > > > sample data on the CDROM to 12 bit linear in order to dump 
> the 
> > > > samples into the Emax. The Emax would then have to convert 
the 
> 12 
> > > bit 
> > > > linear samples 
> > > > > back to compressed 8 bit samples. The transfer of samples 
> would 
> > > > also take 50% longer for 12 bit linear compared to 8 bit 
> > > compressed. 
> > > > And of course 
> > > > > there would be no way for sequencer data included in the 
bank 
> > to 
> > > be 
> > > > loaded into the Emax. I could be wrong, but it just seems 
> > unlikely 
> > > > Emu would have 
> > > > > made it so difficult when a small software update to the 
Emax 
> > > could 
> > > > make bank dumping work in much the same way as the EII.
> > > > > 
> > > > > >
> > > > > 
> > > > > Nevertheless I will still do some experiments to find out 
if 
> > the 
> > > > Emax 
> > > > > OS doesn't have any "fast bank load" commands... 
> > > > > By the way: does anyone know whether the binary code of the 
> > Emax 
> > > OS 
> > > > > can easily be de-compiled/disassembled in some way in order 
> to 
> > > get 
> > > > > some kind of source code ? Is a simple Z80 disassembler 
> > > sufficient ?
> > > > > 
> > > > > 
> > > > > 
> > > > > 
> > > > > Unfortunately it seems the only way is to experiment and 
see 
> > what 
> > > > can be uncovered. The Emax NS32000 main CPU code can be 
> > > disassembled 
> > > > but it is 
> > > > > not a common processor. The hard part of analyzing the 
> > > disassembled 
> > > > code is working out where the program and data begins and 
ends 
> as 
> > > > well as what 
> > > > > interrupt routines are being handled at runtime and how 
they 
> > > > interact. You would need to combine together the code from 
the 
> > disk 
> > > > OS image and the 
> > > > > EPROM into a processor memory map. Various hardware 
> peripherals 
> > > > will also probably exist at certain addresses in the memory 
> map. 
> > To 
> > > > pull it all 
> > > > > together you will ideally have the circuit schematics, the 
> > memory 
> > > > map, CPU/chip documentation plus a detailed design 
description 
> of 
> > > how 
> > > > the system 
> > > > > works. Often much of this data can be found in the product 
> > > service 
> > > > manual. Then you need to determine which routines are called 
> when 
> > > > MIDI/RS422 
> > > > > interrupts are handled. Testing with a logic analyzer 
probing 
> > the 
> > > > CPU would certainly make that easier.
> > > > > 
> > > > > /Tristan
> > > > > 
> > > > > >
> > > > > 
> > > > > 
> > > > > ///E-Synthesist 
> > > > > 
> > > > > --- In emax@yahoogroups.com, tu@ wrote:
> > > > > >
> > > > > > That seems excessively slow, as the EII could load a 
> similar 
> > > > sized 
> > > > > bank from the same CDROM 
> > > > > > drive in 12 seconds. Its hard to imagine Emu would not 
have 
> > > > > implemented a similar load time on 
> > > > > > the Emax if all it took was adding a software routine. 
But 
> > then 
> > > > > again, stranger things have 
> > > > > > happened...
> > > > > > 
> > > > > > /Tristan
> > > > > > 
> > > > > > Quoting John Silveria II <john@>:
> > > > > > 
> > > > > > > Somewhere, and I can't remember where, I read that the 
CD-
> > Rom 
> > > > > drive
> > > > > > > took 
> > > > > > > up to 5 minutes to load a bank. I wish I could remember 
> > > where. 
> > > > So
> > > > > > > indeed 
> > > > > > > it was not only as slow as typical SYSEX load, it could 
> > > > actually 
> > > > > take
> > > > > > > 
> > > > > > > longer.
> > > > > > >
>