Technical Bulletin - MS-124 Rev T0 (9/11/92)
This is a special version of the MS-124 MIDI to Serial Interface for general purpose MIDI output applications.
Specifications are identical to the MS-124 with the following exceptions:
- MIDI Input is deleted.
- All RS-232 outputs are deleted - no handshaking is required.
- Port addressing is deleted - all four ports output the same data.
- Real-time clock output is deleted.
- Baud rate is switch selectable - A = 19200, B = 9600.
- The M/S switch is disabled.
- Serial Input Word - 1 Start, 8 Data, No Parity, and 1 Stop Bits.
Application programs need only to set the serial port to the
proper baud rate and word structure. Data is simply passed on a
byte by byte basis, no protocols, handshaking, or other
interactions are required. The MS-124 performs a real-time baud
rate conversion with absolutely minimal time delay. MIDI data
transmission is actually completed before the end of the incoming
If the interface is to be serial port powered, both RTS and DTR should be asserted. A delay of 300 mS should occur after assertion to allow the power supply to stabilize. Resetting both RTS and DTR will reset the interface after a minimum time delay of 200 mS. Asserting RTS or DTR alone will not supply sufficient power for more than two MIDI Outputs. If external power is used, the state of RTS and DTR is ignored.
The interface is configured as limited Data Communication
Equipment (DCE). The minimum cable requirements are GND (7) and
TXD (2). If serial port power is used, RTS (4) and DTR (20) must
also be connected. Chassis Ground (1) may optionally be
connected. No other signals are used by the MS-124. Cable
requirements of the host system may be more complex, depending on
the system software primarily. If hardware handshaking is
required, "loopback" connections may be required at the
host serial port connector. Refer to the appropriate system
manuals (both hardware and software) for the particular details.
If the host system port is configured as a terminal (DTE), a "straight" serial cable will generally work, while a "null" cable will be required for a DCE host. The interface can be easily tested using any program capable of sending 8 bit binary data to the serial port. Nearly any Debugging program can be used to output data directly to the port UART, if more elegant software is not available. MIDI data can be monitored using a PC monitor program such as Key Electronics MIDI MonKEY and MS-101, 103, 114, or 124 interface.
Copyright (c) MIDIator Systems, 1999