7700 MultiFrame Manual
7707DT RS-232/422/485 Fiber Data Transceiver
Page - 24
Revision
1.8
7.
APPENDIX - MPK ROUTER CONTROL INTERFACE TO 7707DT
7.1. OVERVIEW
Philips Broadcast implemented the MPK (message per keystroke) interface protocol for control panels
used in Jupiter router systems. Grass Valley has since become responsible for the Jupiter series of router
systems. The MPK control interface uses a proprietary method of signaling, for which special
considerations are required when connecting to other interface types. This application note describes
methods for using the 7707DT Fiber Data Transceiver to transport MPK control signals.
The 7707DT series Fiber Data Transceivers communicate bi-directional RS-422 and RS-485 data signals
over a single fiber optic link. By methods described herein, the MPK interface protocol is also
accommodated. The user must first note that the MPK interface protocol is different from RS-422 or RS-
485.
RS-422:
Two devices send data separately in each direction between them. Data in each direction is
carried over a balanced pair of wires. Each of the two devices is always transmitting data to
the receiver of the other device. Figure 7-1 shows an RS-422 connection between two
devices.
RS-485:
Each of two or more devices sends and receives data separately over a shared balanced
pair of wires. At any one time, only one device can transmit data. This avoids contention of
the shared pair of wires. Each device takes turns transmitting data. While not transmitting
data, the interface of each other device is in a high-impedance state, and receives input
data. Data from the transmitting device is broadcast to all other devices. Each other device
must process data being received, and realize its turn to transmit data. By this method,
several devices can communicate data between each other using the same balanced pair
of wires. Figure 7-2 shows an RS-485 connection between four devices.
MPK:
This is a proprietary interface protocol used to communicate between Control Panels and
System Controllers of the Jupiter router system. One port of a System Controller (such as
the VM-3000) communicates with one or more Control Panels. The method of data transfer
in the System Controller to Control Panel direction is different from that in the Control Panel
to System Controller direction. Figure 7-3 shows an MPK connection between a System
Controller and three Control Panels.
The System Controller broadcasts data to one or more Control Panels. One balanced pair
of wires connects output data from the System Controller to all Control Panels. The
interface protocol in this direction is similar to RS-422, in that the System Controller is
always transmitting data to the Control Panel inputs.
Each Control Panel must be able to send data back to the System Controller. For this
purpose, a single balanced pair of wires is shared between all Control Panels. At any one
time, only one Control Panel can transmit data. This avoids contention of the shared
balanced pair of wires. Each Control Panel takes turns transmitting data. While not
transmitting data, the interface of each other Control Panel is in a high-impedance state.
The interface protocol in this direction is similar to RS-485, in that each Control Panel takes
turns transmitting data to the System Controller over a shared balanced pair of wires.
