RX01 / RX02     8" floppy disk drive
RX11 / RX211   controller

Direct jumps to:
  • «-»    General disk drive information
  • «-»    Available documentation
  • «-»    RX02 configuration modes
  • «-»    RX01/RX02 floppy disks
  • «-»    UNIBUS interfaces (M7846, M8256)
  • «-»    Controller diagnostics
  • «-»    RX11 (M7846) bootstrap data
  • «-»    RX211 (M8256) bootstrap data
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Floppy disks on these old machines are 8 inches in size and exist in single and double density.
High density was not yet invented.

The RX01 has two 8" drives capable of single density only.
Inside the drive are two boards: a controller (M7726) and a read/write board (M7727).
Through an interface board this RX01 was connected to the computer system.

    full size RX01 option bulletin (785x1038 pixels, 284 kb)

The RX02 has also two 8" drives, but can read and write double density floppies. The two boards inside this drive are the controller (M7744) and the read/write board (M7745). The controller board inside the RX02 has two DIP switches and thus the drive could be configured to work as an RX02 for a PDP-11 (or LSI-11) with data transfer using DMA, as an RX01 for all three systems using programmed I/O data transfer, or as RX02 for the PDP-8 only with data transfer on programmed I/O basis.

full size RX02 User Guide (785x1038 pixels, 625 kb)
The interface logic for the RX01 is the following.

bussystem  subsystem    interface  
  LSIBUS  LSI-11RXV11M7946
UNIBUS  PDP-11  RX11M7846

The interface logic for the RX02 is the following.

bussystem  subsystem    interface  
  LSIBUS  LSI-11RXV21M8029
UNIBUS  PDP-11  RX211M8256

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RX02 floppy disk logo

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RX02 8" floppy disk drive
Startup current for the drive is:
        Drive specifications RX01/RX02        
Height26.67 cm (10.5")
Width19" rack size compatible
Depth43.18 cm (17")
Weight xx kg (60 lb)
Power200 W max (dual drive)

    Data storage capacity    
     RX01        RX02    
Number of surfaces1
Number of tracks/surface77
Number of sectors/track26
  Number of 8-bit bytes/sector  128256
Formatted capacity (bytes)256256512512

The data in the table is for the RX02 drive recording in double density. When the RX02 is set to operate in single density, the RX01 data applies. Although the 8" floppy disk has (how surprisingly) identical measurements, an RX02 floppy cannot be read by a RX01 drive. RX01 floppies are written in single density, whereas RX02 floppies are partly written in double density. The header of a sector is written in single density, but the data in a sector is written in double density. That is why 'normal' floppy disk controllers cannot read RX02 floppies.

    Drive performance (timing)    
Time for half revolution 83 mSec
Diskette rotation speed 360 RPM
One track move (mSec) 106
Average track seek time   380 mSec     262 mSec  
  Maximum track seek time   760 mSec 
Head settling time (mSec) 2025
The diskdrive interfaces to the UNIBUS with the
    ° M7846 (RX01 controller) or the
    ° M8256 (RX211 controller)
via a 40-wire flat ribbon cable with a length of 15 foot (4.57 meters).

The DEC partnumber is BC05L-15.

The RX02 disk drive can be modified to read and write RX01 formatted floppies. In the drive on the internal controller board (M7744) is a 2-way DIP switch.

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RX02 controller board M7744 The upper board inside the RX02 drive is the M7744 controller.

full view of the M7744 board (122 kb)

In the middle of this board is a 2-way DIP switch.
Click on the image at the right for more detail.
With these DIP switches the RX02 drive can be configured into the following modes of operation:

subsystemsystem  S1-1     S1-2   *  
RX211   RXV21 PDP-11   LSI-11OFFONnote 1
  RX8E   RX11   RXV11     PDP-8   PDP-11   LSI-11  ONOFF note 2
RX28PDP-8 onlyOFFOFF   note 2  

      * note 1: data transfer using DMA
      * note 2: data transfer using programmed I/O
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RX02 8" floppy disk (528 kb) The media used on the RX02 floppy disk system is compatible with the IBM 3740 family of equipment. The diskette is encased in a plastic envelope with a large slit for the read/write head, a centre hole for the drive spindle hub and a hole for track index sensing. The diskette is soft-sectored, and the media is preformatted in an industry-standard compatible format.

If you have a system with an RX02 installed, you can "reformat" RX01 disks. The formatting process, however, is not actually a real "format writing". It accepts a pre-formatted disk with the 128-byte single density data sectors (and the single density headers), and rewrites the data sectors as 256-byte block sectors.


RX01 8" floppy disk controller The RX11 UNIBUS controller for the RX01 drive has the number M7846 on the handle.
Here should come an explanation, XXXXXXX, the chips on the board, etc.

RX11 jumper locations
Note that the RX01 is a polled-I/O device, so the NPR wire must be intact!

The RX211 UNIBUS controller is for the RX02 drive and has M8256 on the handle. RX02 8" floppy disk controller The RX211 controller board for UNIBUS has the code M8256.
The default CSR, (Command & Status Register - the base address), is 177170 (octal of course) and this is set by the 10-way DIP switch. SW1 is on the left and is for A3, SW10 is for A12.
When the switch is in the "off" position it represents a binairy '1'.
So the standard RX211 address is 1111001111 on this DIP switch. The 10-way DIP switch is in the picture at the bottom on the opposite side of the BERG connector which accepts the flatcable going to the drive.
RX211 jumper locations
The 7-way DIP switch is for setting the interrupt vector. For the RX211 it defaults to 264.
When the switch is in the "off" position it represents a binairy '0'.
SW1 is vector bit 2, SW7 is vector bit 8. So the standard RX211 vector is 1011010 on this DIP switch. This 7-way DIP switch is located between the backplane connectors C and D.

The priority level is standard set to BR5 and can be changed by inserting another plug in the socket located near backplane connector D and below the 7-way DIP switch.

As the RX02 is normally configured as a DMA device you must cut the NPR jumper on the backplane for the slot where the M8256 is seated. The NPR jumper wire is on pins CA1 - CB1.
The M8256 controller represents 2 bus loads on the UNIBUS, and needs 1.8 A. maximum at 5 Vdc.
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The RX11 (M7846) subsystem has two diagnostics:

«-»     ZRXA(x)    system reliability test
«-»     ZRXB(x)    interface diagnostic

The RX211 (M8256) subsystem has four diagnostics:

«-»     ZRXD(x)    RX02 performance exerciser
«-»     ZRXE(x)    RX02 formatter program
«-»     ZRXF(x)    RX02 function/logic
      ZRXC(x)    RX02 utility driver (Brutus)

The (x) represents the revision level.
ZRXC is primarily an engineering tool, ZRXE set media density only and does not write headers.
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Loading or toggling in this data enables the PDP to boot from the floppy disk.
This bootstrap is taken from the RX01/RX02 Pocket Service Guide, EK-RX012-PS-002.
As I have not (yet) connected the RX11 controller with the RX01, I can not check this code at the moment. It requires a system generation if you want to have two floppy disk controllers in a single system. I want to add the RX11 to the RX211 which is already in the PDP-11/35. If I only had time ....

    How to load a bootstrap program and start the execution.

The start address is 001000.



Loading or toggling in this data enables the PDP to boot from the floppy disk.
This bootstrap is taken from the RX01/RX02 Pocket Service Guide, EK-RX012-PS-002.
I have entered this code and my PDP-11/34A and my PDP-11/35 just boot fine.

    How to load a bootstrap program and start the execution.

The start address is 002000.

  x0x2x4x6 x0x2x4x6
002000012701177170012700100240 005002012705000200012704
002020000401012703177172030011 001776100440012711000407
002040030011001776100433110413 000304030011001776110413
002060000304030011001776100422 012711000403030011001776
002100100415010513030011001776 100411010213060502060502
002120122424120427000007003737 005000005007000000