The confusing world of RS422 and RS232
How do Lumberjack and Takelog talk to my recording machine(s)?
Most computers are fitted with one 9-pin RS232 serial port. However, the standard Sony P2 machine control format used by Lumberjack and Takelog requires an RS422 port. The names may sound similar, but they are different! The main difference is that RS232 is an unbalanced system, with two wires for the data (one to send, and one to return), whereas RS422 is balanced, with four wires (a 'positive' and 'negative' send, and a 'positive' and 'negative' return).
Lumberjack has the added benefit/problem of being able independently to control up to 4 machines - which requires 4 serial ports.
There are two main ways of dealing with these problems:
If your computer has the capability, I would recommend a USB solution. USB boxes can be "hot-plugged", are easy to install, and very convenient.
Please note, for all these solutions, that the computer industry standard wiring convention for 9-pin RS422 ports is not the same as the broadcast industry standard. Some manufacturers (unfortunately only a very few) provide RS422 cards/boxes with the broadcast standard wiring. See below for the broadcast pinout. If you use a non broadcast industry standard device, you will need a custom adaptor cable.
The cheapest PCI solution I have found so far is from Data Solutions, who can supply the excellent DC-0032 4-port RS422 PCI card for £91.
Both of these products are strongly recommended. Custom cable wiring for each of these solutions is shown here.
An alternative is to build a converter yourself. Click here to see the circuit diagram of a simple converter that has been used successfully at Abbey Road Studios for many years. Note that the RS232 handshake lines are looped straight back (DTR to DSR, and RTS to CTS).
Important Note about Line Termination
Some recording machines, such as the Sony 7030 range of DAT machines, have a 100R termination resistor fitted in their 9-pin input (i.e. where the data comes in from the computer). This is a fairly low value, which results in a reasonably high current flowing through the line.
The net result of all this is that the power supply of the RS422 driver needs to be capable of supplying this current. Many of the commercially available RS232 to RS422 converters are powered from the RS232 port on the computer, which generally do not have the guts to cope with powering a converter and a high current line.
In my experience, if you are driving a machine fitted with a 100R termination resistor using an RS232 to RS422 converter, then the converter will always need an external power supply, rather than being powered from the computer's RS232 port.
Most of the Sony video machines do not have terminating resistors, and these can be driven using "port-powered" RS232 to RS422 converters. The Tascam DA-88 tape machine also does not have terminating resistor. Fostex DAT machines have a switchable terminating resistor - I suggest leaving it OFF.
Power supply considerations for the RS422 driver circuitry are especially important if you opt to drive more than one machine from a single port (see below).
The following tables shows the pin connections for Sony P2 compatible tape machines, and standard IBM-PC 9-pin RS232 serial ports:
Running more than one machine from a single RS422 port
It is possible to control more than one machine from a single port. The general principle is to send commands from the computer to multiple machines, but only let the computer receive return data from one of the machines (the "master"). Thus the displays in Takelog and Lumberjack (e.g. machine position and transport status) will only show information for the "master" machine. But if the software sends a command (e.g. "Play"), all listening machines will respond.
You will need to make up a custom cable, where pins 2 and 7 of the RS422 line (the recording machine's Transmit lines) are only connected for the designated "Master" machine.
If the machines used do not have terminating resistors on their incoming lines (pins 3 and 8 - the Receive lines) there is no practical limit on how many machines can be controlled. However, if the machines do have 100R terminating resistors, then please be very careful. Connecting 4 machines together like this will result in the computer's RS422 driver trying to drive a 25R load - almost a short circuit. With some cards/computers/converters, this can destroy the RS422 driver circuitry. You have been warned! The do-it-yourself circuit shown here has been used to drive 4 terminated devices in parallel for many years without failure.
Companies manufacturing and selling RS232 and RS422 products
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