I/O operations with special functions

Besides the "normal" use of the I/O operations for data transfers, these operations are also used to control special functions within the machine, e.g. the processor or the display adapter, or to set special flags. These functions are listed below. If a functions should only be valid either for the 5100 or for the 5110 it will be marked in the first column.

Device 0 (Processor, Display adapter)

Control

Put (only 5110)

OpE

The I/O operations perform the shift and rotate instructions of the processor.

Device 1 (Common / Language ROS)

Control

To read out the selected ROS the desired address is sent to device 1 with two consecutive PUTB instructions, first the high-byte of the address, then the low byte.
ATTENTION: The address is the word address, not the byte address!

Then the word can be read with two GETB instructions. The second GETB will automatically increase the internal address counter by 1 so you don't have to reload the address when reading a contiguous area.

The current ROS address can be read back with two STAT instructions.

Bit 0 is very interesting: the ability to write to the ROS (or the writable substitute) was apparently used by the developers to test new versions of the non-executable ROS' without the need to burn dozens of EPROMs (we're in the time of 1702s or 2708s!) or create new mask ROMs.

Device 2 (Executable ROS)

only 5110

Control

Since only one of the two executable ROS' (I/O routines, meta-interpreter) can be active, this control instruction provides a means to switch between these two. Note that the selection between APL or BASIC executable ROS is done in hardware with the APL/BASIC switch on the front plate.
Obviously there needs to be a transfer subroutine in each of these ROS modules since execution will transfer to the other ROS immediatley following the control instruction.

OpE

OpE gives you one of three status bytes, the selection is done by presetting the destination register (the values in brackets are for the 5110 model 1 APL/BASIC without Feature ROS):

   $80 - Size of the I/O ROS [= $F0]
   $40 - Size of the meta-interpreter ROS [= $C0]
   $20 - (??) [= $80]

• The I/O ROS occupies the range 0000-7FFF
• The optional Feature ROS (Diskette Sort Feature) is at 8000
• The APL ROS is 20kB and occupies the range 0000-4FFE
• The BASIC ROS is 16kB and occupies the range 0000-3FFE

Device 4 (Keyboard / Interrupt 1 control)

Control

OpE

The keyboard offers a status byte and a scancode. The selection is done by presetting the destination register for the STAT instruction:

   $80 - Read status
   $40 - Read scancode

Status byte

This is the status byte read via an OpE instruction.

Device D (Diskette adapter)

Control

Put

The mechanical operations of the disk drive can be controlled while in Access Mode of the controller. Following are the functions:

During Reset Mode a PUT instruction transfers the desired subdevice address to the diskette controller to select one of the maximum four possible drives.

In Write Mode PUT instructions are used to transfer the data bytes to the diskette.

Get

In Access Mode GET fetches the status byte of the disk drive, not of the diskette adapter (see OpE for this).

OpE

OpE fetches the status of the diskette adapter.

Device E (Tape adapter)

Control

Put

The following description comes from the IBM 5100 MIM page C-14, but it is also valid for the 5110.

OpE

This returns the tape status byte, but you need to follow these steps:

• Reset adapter with CTRL $E,#$FF
• Read in dummy byte e.g. with GETB R5,$E
• Preset destination register with $40

  CTRL $E, #$FF
  GETB R5, $E
  LBI R5, #$40
  STAT R5, $E
  MOVE $8E, R5    ; Store status in 008F (see MIM page 3-34)

Device F (selective reset of individual devices)

Control