Ref: 99980068 Title: RFM/5 Station Mgmt Interface and Automatic Level Control Date: 8/1/86 Copyright 3Com Corporation, 1991. All rights reserved. Introduction The RFM/5 is an intelligent microcomputer-controlled broadband modem for use with the Bridge Communications Series 1 and Series/ 200 Broadband Communications Servers. In addition to configuring system-specific Radio Frequency parameters, the station management interface allows the user to investigate modem transmit and receive levels. Operation of the station management interface requires the use of a terminal adapter available from Bridge Communications. This device breaks out the asyncrhonous communications path between the modem and the server and converts the signal voltage for use with a standard CRT. In the future, these commands will be available from the Bridge Communications Server or Network Control Server User Interface. The terminal used to communicate with the RFM/5 must be configured for 9600 baud, 8 data bits, and NO parity. It is connected to the 25-pin D connected on the terminal adapter by means of a standard one-to-one cable (the adapter looks like a DCE device). The adapter is installed at the RFM/5 in line with the server cable and is powered by the server. The adapter should be installed with the server power off. Once the terminal is connected and the adapter is intalled and powered on, pressing RETURN should cause the modem prompt to appear as follows: RFM/5> When the prompt is displayed, the RFM/5 is ready to accept commands. The Show Status Command In addition to the current transmit and receive signal levels, the show status command displays the configuration parameters of the RFM/5. The format and display of this command are as follows: sh status .br;Model RFM/5 .br;Version R9 RFM5 Revision 01A .br;Date of Manufacture - 08/86 .br;Hardware Revision - 01 .br;Training Program Revision - 1 .br;Transmit Channel - 1 .br;Receive Channel -1 .br;Nominal Transmit Level - +45 dBmV .br;Minimum Transmit Level - +35 dBmV .br;Maximum Transmit Level - +52 dBmV .br;Current Transmit Level - +45 dBmV .br;Current Receive Level - ~+02 dBmV RFM/5> The first five lines display general configuration information, the model number, firmware revision, data of manufacture, hardware revision, and training program revision. Most of the displays are self-explanatory, but the training program is used during manufacturing to calculate and store modem-dependent variables necessary to provide accurate signal level measurement and control. The next two lines show the current transmit and receive channels. These displays can be modified using the "set chan" command. The channel numbers and operating frequencies are displayed as follows: Channel Transmitted Frequency Received Frequency 1 4A' R 2 5' S 3 6' T 4 FM1' U 5 FM2' V 6 FM3' W 0 Special Programmable channel not yet implemented The next three lines in the display show the transmitter level control parameters. The nominal value is set at power on and should be the same as the broadband network outlet transmit level design specification. This can be thought of as the "Manual" level control value or the level at which the RFM/5 should transmit if the broadband network was perfectly aligned. The minimum and maximum values are limits that can be set to control the amount of adjustment. These limits allow the user to confine the transmitter output to a range as narrow or wide as the user application requires. This prevents the automatic level control features of the Bridge network from causing undesirable interference to other services on the network in the case of a broadband network malfunction. These values can be modified by using the "set notx", "set mitx", and "set matx" commands. The last two lines show the current "real time" transmit and receive signal levels. At room temperature and nominal power supply voltages, these readings are accurate to about +/- 1 dB. The receiver has a range of -15 dBmV to +15 dBmV. If the signal is out of this range, the RFM/5 displays <-15 dBmv or >+15 dBmV as appropriate. For example, when the RFM/5 is not connected to the broadband network, it will report the receive level as <-15 dBmV. The Set Channel Command The user can configure the RFM/5 to operate on any one of six broadband channels by using the set channel command. The valid channels are 1, 2, 3, 4, 5, and 6 as shown in the chart above. To change channels, enter the following command at the prompt: set chan = X where X is 1, 2, 3, 4, 5, or 6 The RFM/5 will then go off-line (you may be able to hear the relay click) for two seconds, change operating frequencies and return on-line. The channel of operation, along with the other configuration parameters, is stored in a non-volatile EEPROM memory in the RFM/5 and will remain set until changed by the user. The Set Transmit Level Parameter Commands Three similar commands are used to set the NOMINAL or power on transmist level in addition to the MINIMUM and MAXIMUM control limits. These changes should only be made by the broadband system manager since improper settings can cause unreliable operation of the RFM/5 and the automatic transmit level control features. These values are factory set at the levels as shown in the status display above and should be optimal for most broadband networks. These three commands are as follows: .br;set notx = XX set nominal transmit level .br;set mitx = XX set minimum transmit level .br;set matx = XX set maximum transmit level where XX = 21 to 52 The transmitter output is adjustable over a 32 dB range from +21 to + 52 dBmV. Automatic Transmit Level Control The automatic transmit level control feature of the RFM/5 works in conjunction with the CR/5 (Channel Remodulator) at the broadband network headend. When the RFM/5 is initially powered on or reset by the server, it sets its transmitter output to the level stored by the "set notx" command. Each time the RFM/5 transmits, its signal level is measured by a precision circuit in the CR/5. The CR/5 compares this level to a range of acceptable values that is set by the broadband network manager on rear panel switches. If the level is out of the acceptable range, the CR/5 sets a contro bit to indicate that the RFM/5 level was too high or too low. As the incoming packet is being repeated by the CR/ 5, it inserts an inband command sequence containing these control bits in the repeated packet. The RFM/5 uses the coincidence of reception of the command sequence and the condition that it is transmitting to "address itself" and pays attention to the level control bits. The RFM/5 applies the "too high" and "too low" control bits to a counter. When the RFM/5 has been repeatedly told that its transmit level is out or range, it changes its level by 1 dB as long as the level change does not cause the transmitter to operate beyond the minimum or maximum limits. Once a change has been made, RFM/5 disables its level control feature for 10 seconds to prevent rapid changes. Depending on how frequent the transmissions from a given server are, the RFM/5 can change level no faster than 1 dB every 10 seconds or no slower than 1 dB every 3 minutes (assuming station management packets are transmitted every 45 seconds).