D192 is setup to provide one stop bit and parity. Most D192 receiver cards do not care whether they get two stop bits or one stop bit and parity. So this fact is mostly irrelevant, except for the few tricky systems which may care. Keep this in mind when troubleshooting Response 2212 interface problems into D192 speaking racks. You may have to enable or disable two stop bit strapping depending on the situation.Also, keep in mind that because it receives D192, it does not necessarily mean it is a D192 rack. Likewise, just because it is a D192 rack, it does not mean it receives only D192. D192 is a model name as well as a protocol. D192 racks may speak either D192 or DMX depending on whether or not the receiver card has been modified.
|5 Pin XLR Pinout|
D192 has the following parameters:
Patchman 27880-(xx) I/O CMX, 8 data bits, 1 start bit, 1 stop bit, even parity, 156.25 kbaud
Prestige, Scenemaster 60 CMX/DMX, 8 data bits, 1 start bit, 2 stop bits, no parity, 156.25 kbaud/250 kbaud
108 Ch. D/A 8 data bits, 1 start bit, 1 stop bit, even parity, 156.25 kbaud
D192 Pack, D192 Rack, Universal D/A, 8 data bits, 1 start bit, 1 stop bit, even parity, 156.3 kbaud
Note: The difference in the clock rates is not enough to cause the UART on the receiver to lose a data bit within a single frame. The last stop bit will slip by in just over one clock period without confusing the UART.
Obviously, many different installation setups can be done. Here are the generalities. Termination, when done, is accomplished by strapping a 100 ohm resistor across data terminals on the right hand side of the rack. This may be difficult to see in some situations as the resistor may be pushed up behind the terminal strip. In some facilities, several runs of DMX data cable may be home runned to the same data terminals in the rack. One way around this is to try and daisy chain runs with spare pairs. Another fix is to remove termination in the rack and then terminate each end of the DMX line with 100 ohm resistors at the plug in plates. This will create a legal RS485 line with the racks as receivers in the middle of the run as long as there are only two runs to the rack. Multiple runs will require daisy chaining and/or retermination.
Converting to DMX:
It is possible to convert D192 control cards to receive DMX. As these cards are essentially state machines, (meaning they rely only on gate values as opposed to having a processor), swapping the oscillator and a time out resistor are all that is needed. The oscillator on the card is 2.4576MHz and should be replaced with 4.0MHz (ETC P/N:Y112). Also, the digital signal time out resistor, denoted R4, is located in the middle front of the card. One of two different values may be seen here, either a 200kohm or a 150kohm. Either of these are thought to be too close in timing and may cause sporadic timeouts in the cards resulting in flickering, flashing, or chasing lights. Note that this resistor value may be the reason D192 systems can not handle high DMX refresh rates even though they were new from the factory. It should be replaced with a 75kohm resistor. This can also be accomplished by paralleling the existing resistor with a 150kohm resistor (ETC P/N:R114). Customers can contact Steve Short at Litetrol to upgrade control modules to DMX on an exchange program. PH: 1-800-548-3876
Known Issue Interacting with Analog House Light Systems:
ETC has seen DMX amplitude drop significantly with D192 systems that also have analog house light systems attached to the rack. The Universal Analog Interface uses a comparator that draws more current and pulls down the DMX voltage when other racks are applied. Additionally, the UAI terminates the data line whenever energized. This termination can not be removed and does not appear when the racks are powered down as termination is performed through a power-sensing relay. It should function acceptably. Scope the DMX signal to make sure it looks good other than the drop in amplitude and do not terminate the data line elsewhere in the system unless this card is removed.