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Application Note·BNC-AN-007 Rev A·October 2026·dc-62022201

Fast Control Port with MDR 26-Pin Connector (Model 825-M)

The Model 825-M Signal Generator can be controlled over an additional parallel port for fast, time-critical settings such as frequency changes. This application note explains how to configure and drive the Fast Control Port, which is included with option FS.

Application Note·BNC-AN-007 Rev A·October 2026·dc-62022201
Contents
  1. 1Introduction
  2. 2Configuring the FCP
  3. 38-bit Mode
  4. 416-bit Mode
  5. 5Electrical Specification
  6. 6Cable Assembly
  7. 7Further Documentation

1Introduction

For fast, time-critical settings such as frequency changes, the Model 825-M can be controlled over the Fast Control Port (FCP), which is included with option FS on single-channel and multi-channel (825-M-20-X, one to four channels) units. It is a parallel port that operates in either 8-bit mode or 16-bit mode. When activated, the frequency and/or amplitude of the RF outputs are controlled by the FCP: the controller addresses a memory and fills it with frequency or amplitude information, and the generator switches as soon as the last byte has been transferred.

To enable and configure the communication over FCP, the device must be configured in advance over SCPI.

2Configuring the FCP

To select the operating mode of the Fast Control Port, the FCP must be configured with an SCPI command:

[:SOURce]:FCPort:MODE 8|8B|8Bits|16|16B|16Bits

Configures the operation mode of the FCP.

*RST value: 16

Further related commands are documented in the Programmer's Manual [1].

38-bit Mode

'8-bit Mode' is limited to frequency control of one RF channel or to a common frequency on several channels. The frequency can either be selected by the index of a pre-defined frequency list or by sending the complete frequency word. On multi-channel devices, it is not possible to operate one channel with a list of frequencies and the other with a frequency word.

Setting the RF frequency and amplitude

The RF output signal can be configured via the FCP with

  • The frequency word (FW). It is 48 bits wide, unsigned, and is calculated as FW = Frequency in Hz * 256.
  • The amplitude word (AW). It is 16 bits wide, signed (two's complement), and is calculated as AW = Amplitude in dBm * 128.

8-bit mode is limited to only one set of one frequency and one amplitude word. All channels with FCP enabled will use the same set.

However, frequency vs. amplitude words may be used individually: one channel (e.g., 3) can be under FCP amplitude control, while another channel (e.g., 2) is under FCP frequency control.

The Signal Generator must be set up to be controlled by FCP with SCPI commands:

[:SOURce#]:FCPort:CONTrol:FREQuency ON|OFF|1|0

Enables or disables FCP frequency control on the specified RF channel

*RST value: OFF

[:SOURce#]:FCPort:CONTrol:AMPLitude ON|OFF|1|0

Enables or disables FCP amplitude control on the specified RF channel

*RST value: OFF

Complete SCPI command sequence for frequency mode:

Table 1. Complete SCPI command sequence for frequency mode
CommandDescription
SOUR<x>Select the RF output
OUTP ONEnables RF output
FREQ <x>Sets initial RF output frequency
POW <x>Sets RF output power
FCP:MODE 8Sets FCP to 8-bit Mode
FCP:CONT:FREQ ONEnables FCP frequency control

For amplitude mode, modify the last command:

Table 2. For amplitude mode, modify the last command
CommandDescription
FCP:CONT:AMPL ONEnables FCP amplitude control

Both modes can be combined to full frequency and amplitude control:

Table 3. Both modes can be combined to full frequency and amplitude control
CommandDescription
FCP:CONT:FREQ ON;AMPL ONEnables combined FCP frequency and amplitude control

The Frequency Word (FW) is written sequentially to address 0 to 11. Writing bit 47 (MSB) of the FW triggers the processing and updates of the RF output signal that is RF Frequency = FW value * 1 Hz / 256.

The Amplitude Word (AW) is written sequentially to address 12 to 15. Writing bit 15 (MSB) of the AW triggers the processing and updates of the RF output signal that is RF Amplitude = AW value * 1 dBm / 128.

In combined frequency and amplitude mode, writing the MSB of both words (global bit 63 = AW bit 15) triggers the update. This ensures simultaneous frequency and amplitude update at the RF output.

Table 4.
AddressData
0FW (frequency word) bits [3...0]
1FW (frequency word) bits [7...4]
2FW (frequency word) bits [11...8]
3FW (frequency word) bits [15...12]
4FW (frequency word) bits [19...16]
5FW (frequency word) bits [23...20]
6FW (frequency word) bits [27...24]
7FW (frequency word) bits [31...28]
8FW (frequency word) bits [35...32]
9FW (frequency word) bits [39...36]
10FW (frequency word) bits [43...40]
11FW (frequency word) bits [47...44]
12AW (amplitude word) bits [3...0]
13AW (amplitude word) bits [7...4]
14AW (amplitude word) bits [11...8]
15AW (amplitude word) bits [15...12]

Timing

Figure 1. Schematic: programming the frequency word over the FCP in 8-bit mode. Twelve address and data nibbles are strobed in, the generator acknowledges each with ACK, and BUSY is raised while the word is processed; setup time t1 and hold time t2 are marked.
SchematicFigure 1. Programming the frequency word over the FCP in 8-bit mode. Twelve address and data nibbles are strobed in, the generator acknowledges each with ACK, and BUSY is raised while the word is processed; setup time t1 and hold time t2 are marked.

Address and data are transferred at the same time. The Signal Generator reads the data upon a falling edge on the strobe line. The Signal Generator confirms the received data with ACK and informs the controller by the BUSY signal while processing the information.

Signals: Address A<3..0>, Data D<3..0>, STROBE, ACK, BUSY

Table 5.
ParameterValue
Setup-time t1> -10 ns
Hold-time t2> 60 ns

SCPI & FCP Example

This is an SCPI example to set the RF output frequency of RF output 2 on a multi-channel system:

Table 6. This is an SCPI example to set the RF output frequency of RF output 2 on a multi-channel system
CommandDescription
*RSTReset device
OUTP2 ONEnables RF output 2
POW 5Sets RF output power to 5 dBm
FCP:MODE 8set FCP to 8-bit Mode
SOUR2:FCP:CONT:FREQ ONEnables FCP on RF output 2
*OPC?Check if the operation is complete

After configuring RF channel 2, writing FW 256,000,000,000 to the FCP produces a 1 GHz RF signal (1 GHz × 256).

FCP:CONT:FREQ ON must be enabled on each channel to provide the same frequency on multiple channels.

Selecting pre-defined RF Frequency

The device plays points from a pre-defined list of frequency settings with up to 20,000 entries in this mode. It is similar to a list sweep, with the FCP selecting the pre-defined frequency.

8-bit mode is limited to only one list word. All channels with FCP enabled will use the same list word.

However, the frequency list of each channel can be configured individually: e.g., point 1 can be 1 GHz for channel 1 but 2 GHz for channel 2.

The Signal Generator must be set up to be controlled by FCP with an SCPI command:

[:SOURce#]:FCPort:CONTrol:LIST ON|OFF|1|0

Enables or disables FCP on the specified RF channel

*RST value: OFF

Complete SCPI command sequence to set up RF output to play selected frequency point:

Table 7. Complete SCPI command sequence to set up RF output to play selected frequency point
CommandDescription
SOUR <channel>Select the RF output
OUTP ONEnables RF output
POW <x>Sets RF output power
LIST:FREQ <f1>,<f2>,<f3>,...,<fn>Defines a list of frequency settings
FCP:MODE 8Sets FCP to 8-bit Mode
FCP:CONT:LIST ONEnables FCP control

To select a pre-defined frequency, a 16-bit data list word (LW) must be written to address 0 to 3. Writing bit 15 (MSB) triggers the processing and update of the RF output signal. Writing 1 to the list word (LW) plays <f1>, LW = 2 plays <f2> etc.

Table 8.
AddressData
0LW (list word) bits [3...0]
1LW (list word) bits [7...4]
2LW (list word) bits [11...8]
3LW (list word) bits [15...12]

Timing

Figure 2. Schematic: sending a list word over the FCP in 8-bit mode. Four address and data nibbles are strobed in with ACK and BUSY handshaking; setup time t1 and hold time t2 are marked.
SchematicFigure 2. Sending a list word over the FCP in 8-bit mode. Four address and data nibbles are strobed in with ACK and BUSY handshaking; setup time t1 and hold time t2 are marked.

Address and data are transferred at the same time. The Signal Generator reads the data upon a falling edge on the strobe line. The Signal Generator confirms the received data with ACK and informs the controller by the BUSY signal while processing the information.

Signals: Address A<3..0>, Data D<3..0>, STROBE, ACK, BUSY

Table 9.
ParameterValue
Setup-time t1> -10 ns
Hold-time t2> 60 ns

SCPI & FCP Example

This is an SCPI example to set up RF output 1 and RF output 3 on a multi-channel system to play selected frequency point:

Table 10. This is an SCPI example to set up RF output 1 and RF output 3 on a multi-channel system to play selected frequency point
CommandDescription
*RSTResets device
OUTP1 ONEnables RF output 1
OUTP3 ONEnables RF output 3
POW1 5Sets RF output power to 5 dBm
POW3 7Sets RF output power to 7 dBm
SOUR1:LIST:FREQ 1 GHz,1.5 GHz,2 GHzDefines a list of frequencies
SOUR3:LIST:FREQ 1.2 GHz,1.25 GHz,1.3 GHzDefines a list of frequencies
FCP:MODE 8Sets FCP to 8-bit Mode
SOUR1:FCP:CONT:LIST ONEnables FCP on RF output 1
SOUR3:FCP:CONT:LIST ONEnables FCP on RF output 3
*OPC?Checks if the operation is complete

After successfully configuring RF output 1 and 3, writing 1 to the list word (LW) over the FCP, would simultaneously play

  • 1 GHz on RF output 1 with an output power of 5 dBm
  • 1.2 GHz on RF output 3 with an output power of 7 dBm

416-bit Mode

The '16-bit Mode' extends the '8-bit Mode' with multi-channel support. The frequency can either be selected by the index of a pre-defined frequency list or by sending the complete frequency word. On a multi-channel system, it is possible to operate each channel individually with a frequency list, the frequency, or the amplitude word.

Setting the RF Frequency and Amplitude

The RF output signal can be configured via the FCP with

  • The frequency word (FW). It is 48 bits wide, unsigned, and is calculated as FW = Frequency in Hz * 256.
  • The amplitude word (AW). It is 16 bits wide, signed (two's complement), and is calculated as AW = Amplitude in dBm * 128.

The Signal Generator must be set up to be controlled by FCP with SCPI commands:

[:SOURce#]:FCPort:CONTrol:FREQuency ON|OFF|1|0

Enables or disables FCP to set frequency word on the specified RF channel

*RST value: OFF

[:SOURce#]:FCPort:CONTrol:AMPLitude ON|OFF|1|0

Enables or disables FCP amplitude control on the specified RF channel

*RST value: OFF

Complete SCPI command sequence for frequency mode:

Table 11. Complete SCPI command sequence for frequency mode
CommandDescription
SOUR<x>Select the RF output
OUTP ONEnables RF output
FREQ <x>Sets initial RF output frequency
POW <x>Sets RF output power
FCP:MODE 16Sets FCP to 16-bit Mode
FCP:CONT:FREQ ONEnables FCP control

For amplitude mode, modify the last command:

Table 12. For amplitude mode, modify the last command
CommandDescription
FCP:CONT:AMPL ONEnables FCP amplitude control

Both modes can be combined to full frequency and amplitude control:

Table 13. Both modes can be combined to full frequency and amplitude control
CommandDescription
FCP:CONT:FREQ ON;AMPL ONEnables combined FCP frequency and amplitude control

The Frequency Word (FW) is written sequentially to address 0 to 5. Writing bit 47 (MSB) of the FW triggers the processing and updates of the RF output signal that is RF Frequency = FW value * 1 Hz / 256.

The Amplitude Word (AW) is written sequentially to address 6 to 7. Writing bit 15 (MSB) of the AW triggers the processing and updates of the RF output signal that is RF Amplitude = AW value * 1 dBm / 128.

In combined frequency and amplitude mode, writing the MSB of both words (global bit 63 = AW bit 15) triggers the update. This ensures simultaneous frequency and amplitude update at the RF output.

Table 14.
RF ChannelAddressData
10FW (frequency word) bits [7...0]
11FW (frequency word) bits [15...8]
12FW (frequency word) bits [23...16]
13FW (frequency word) bits [31...24]
14FW (frequency word) bits [39...32]
15FW (frequency word) bits [47...40]
16AW (amplitude word) bits [7...0]
17AW (amplitude word) bits [15...8]
216...21FW (frequency word)
222...23AW (amplitude word)
332...37FW (frequency word)
338...39AW (Amplitude word)
448...53FW (frequency word)
454...55AW (amplitude word)

Timing

Figure 3. Schematic: programming the frequency word over the FCP in 16-bit mode. Six address and data bytes are strobed in and BUSY is raised while the word is processed; there is no ACK in 16-bit mode. Setup time t1 and hold time t2 are marked.
SchematicFigure 3. Programming the frequency word over the FCP in 16-bit mode. Six address and data bytes are strobed in and BUSY is raised while the word is processed; there is no ACK in 16-bit mode. Setup time t1 and hold time t2 are marked.

Address and data are transferred at the same time. The Signal Generator reads the data upon a falling edge on the strobe line and informs the controller by the BUSY signal while processing the information.

Signals: Address A<7..0>, Data D<7..0>, STROBE, BUSY

Table 15.
ParameterValue
Setup-time t1> -10 ns
Hold-time t2> 60 ns

SCPI & FCP example

This is an SCPI example to set the RF output frequency of RF outputs 1 and 3 on a multi-channel system:

Table 16. This is an SCPI example to set the RF output frequency of RF outputs 1 and 3 on a multi-channel system
CommandDescription
*RSTReset device
OUTP1 ONEnables RF output 1
OUTP3 ONEnables RF output 3
POW1 5Sets RF output power to 5 dBm
POW3 7Sets RF output power to 7 dBm
FCP:MODE 16Sets FCP to 16-bit Mode
SOUR1:FCP:CONT:FREQ ONEnables FCP on RF output 1
SOUR3:FCP:CONT:FREQ ONEnables FCP on RF output 3
*OPC?Check if the operation is complete

After configuring RF channels 1 and 3, writing FW 256,000,000,000 to the FCP plays simultaneously

  • 1 GHz on RF output 1 with an output power of 5 dBm
  • 1 GHz on RF output 3 with an output power of 7 dBm

Each RF channel can be given its own frequency word and amplitude word.

Selecting pre-defined RF Frequency

The device plays points from a pre-defined list of frequency settings with up to 20,000 entries in this mode. It is similar to a list sweep, with the FCP selecting the pre-defined frequency.

The Signal Generator must be set up to be controlled by FCP with an SCPI command:

[:SOURce#]:FCPort:CONTrol:LIST ON|OFF|1|0

Enables or disables FCP on the specified RF channel

Complete SCPI command sequence to set up RF output to play selected frequency point:

Table 17. Complete SCPI command sequence to set up RF output to play selected frequency point
CommandDescription
SOUR <channel>Select the RF output
OUTP ONEnables RF output
POW <x>Sets RF output power
LIST:FREQ <f1>,<f2>,<f3>,...,<fn>Defines a list of frequency settings
FCP:MODE 16Sets FCP to 16-bit Mode
FCP:CONT:LIST ONEnables FCP control

For each RF channel, a 16-bit data list word (LW) must be written to address 0 to 1 to select the pre-defined frequencies (see table below). Writing bit 15 (MSB) of a list word 1 triggers the processing and update of the corresponding channel's RF output signal. Writing 1 to the list word (LW) plays <f1>, LW = 2 plays <f2> etc.

Table 18.
RF channelAddressData
10LW (list word) bits [7...0]
11LW (list word) bits [15...8]
216LW (list word) bits [7...0]
217LW (list word) bits [15...8]
332LW (list word) bits [7...0]
333LW (list word) bits [15...8]
448LW (list word) bits [7...0]
449LW (list word) bits [15...8]

Timing

Figure 4. Schematic: selecting a list entry over the FCP in 16-bit mode. Two address and data bytes per channel are strobed in and BUSY is raised while the entry is processed; setup time t1 and hold time t2 are marked.
SchematicFigure 4. Selecting a list entry over the FCP in 16-bit mode. Two address and data bytes per channel are strobed in and BUSY is raised while the entry is processed; setup time t1 and hold time t2 are marked.

Address and data are transferred at the same time. The Signal Generator reads the data upon a falling edge on the strobe line. The Signal Generator informs the controller by the BUSY signal while processing the information.

Signals: Address A<7..0>, Data D<7..0>, STROBE, BUSY

Table 19.
ParameterValue
Setup-time t1> -10 ns
Hold-time t2> 60 ns

SCPI & FCP Example

This is an SCPI example to set up RF output 1 and RF output 3 on a multi-channel system to play selected frequency point:

Table 20. This is an SCPI example to set up RF output 1 and RF output 3 on a multi-channel system to play selected frequency point
CommandDescription
*RSTReset device
OUTP1 ONEnables RF output 1
OUTP3 ONEnables RF output 3
POW1 5Sets RF output power to 5 dBm
POW3 7Sets RF output power to 7 dBm
SOUR1:LIST:FREQ 1 GHz,1.5 GHz,2 GHzDefines a list of frequencies
SOUR3:LIST:FREQ 1.2 GHz,1.25 GHz,1.3 GHzDefines a list of frequencies
FCP:MODE 16Sets FCP to 16-bit Mode
SOUR1:FCP:CONT:LIST ONEnables FCP on RF output 1
SOUR3:FCP:CONT:LIST ONEnables FCP on RF output 3
*OPC?Check if the operation is complete

After successfully configuring RF output 1 and 3, writing 1 to the list word (LW) over the FCP, would simultaneously play

  • 1 GHz on RF output 1 with an output power of 5 dBm
  • 1.2 GHz on RF output 3 with an output power of 7 dBm

Each RF channel can be given its own list word.

5Electrical Specification

Table 21.
ParameterValue
Input signal0 V to 5 V
Input impedance4.7 kΩ
Maximum toggle rate10 MHz
SchematicFigure 5. The 26-pin Mini-D Ribbon receptacle on the generator, with the panel mounting holes and the pin positions. Dimensions in inches with millimeters in brackets.

RFU = Reserved for Future Use. Ports should not be connected.

Table 22.
PinSignal (8-bit Mode)Signal (16-bit Mode)PinSignal (8-bit Mode)Signal (16-bit Mode)
1STROBE (in)STROBE (in)14RFUData 3
2Address 0Address 015RFUData 4
3Address 1Address 116RFUData 5
4Address 2Address 217RFUData 6
5Address 3Address 318RFUData 7
6Data 0Address 419GNDGND
7Data 1Address 520GNDGND
8Data 2Address 621GNDGND
9Data 3Address 722RFURFU
10ACK (out)Data 023GNDGND
11BUSY (out)BUSY (out)24RFURFU
12RFUData 125GNDGND
13RFUData 226GNDGND

6Cable Assembly

For the external wiring of the FCP port, a cable with 26 conductors and MDR-connector is available.

To build a custom cable, the individual components are listed below:

Table 23. To build a custom cable, the individual components are listed below
DescriptionManufacturerPart Number
Connector Plug MDR 26 Pin3M10126-3000PE
Connector Backshell MDR 26 Pin3M10326-3210-006
Cable shielded 26 wire 28 AWG3M3600B/26

The table below lists the mapping of connector pin and wire colors.

Table 24.
PinWire Color (Solid)Wire Color (Band)Comments
1BlackRedtwisted with Pin 20
2BlackWhite
3WhiteBlack
4BlueRed
5RedBlue
6RedWhite
7WhiteRed
8RedBrown
9BrownRed
10BlueBlack
11BlackBlue
12BrownBlack
13BlackBrown
14OrangeRed
15RedOrange
16RedYellow
17YellowRed
18BlackYellow
19YellowBlack
20RedBlacktwisted with Pin 1
21OrangeBlack
22BlackOrange
23GreenBlack
24BlackGreen
25GreenRed
26RedGreen

7Further Documentation

[1] BNC Programmer's Manual for Signal Generators

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