ND-100 front panel

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ND-100 front panel
ND-100 back side of front panel

The ND-100 series computer may be equipped with a front panel that both shows status of the computer and could control the execution of it. The front panel is a free standing device and communicates with the CPU via micro code and internal registers.

A program can communicate with the front panel via the two special registers PANS and PANC and the privileged instructions TRA 0 and TRR 0.

PANC - Panel Control Register

The Panel Control Register is used to send commands to the Panel Processor, PAP together with data. The PACR is a fifo that is shared by micro program. The status bit Command Ready in PANS should be checked after sending a sequence of commands.

  • Bit 13 : READ. If set the command is a request for data which will be written to the PANS register.
  • Bit 11-12 : Must be zero for macro code program.
  • Bit 8-10 : PCOM, Panel Command Code.
  • Bit 0-7 : WPAN, data sent to PAP.

PANS Panel status register

The Panel Status Register is used to receive data and check the status of the PAP from macro program.

  • Bit 15 : PAN PRES, set to 1 if the front panel is present.
  • Bit 14 : PANC -FULL, when 0 the PANC fifo is full. If status stay at 0 for more than 2ms then the PAP is not working.
  • Bit 13 : READ, if 1 then the last command PAP processed was a read, data is in bit 0-7.
  • Bit 12 : COM RDY, The command in PCOM has been processed.
  • Bit 11 :
  • Bit 8-10 : PCOM, the last command processed.
  • Bit 0-7 : RPAN, Read data from PAP requested via the PANC register. If no read requested then it is a copy of WPAN data.

Panel commands

There are seven legal PAN commands.

 000  Illegal
 400  Future extensions
1000  Message append (write only)
1400  Message control (write only)
2000  Write/Update low seconds (write and read)
2400  Write/Update high seconds (write and read)
3000  Write/Update low days (write and read)
3400  Write/Update high days (write and read)

Message on Function Display

By using the Message control (PCOM=3) and Message append PCOM=2) panel commands it is possible to send text to the front panel. It takes ascii characters that is placed in a buffer of 40 characters that could be rotated to show the message on the front panel. Message control together with WPAN gives these commands

1400 STOP rotation
1401 ABORT, return display to OPCON
1402 INIT, clear text buffer and function display. Prepare for text to be appended.
1404 ROT, rotate the text buffer on the function display
1406 INIT and ROT

After a message has been displayed the display should be handed back to OPCON, therefore all messages should be terminated with ABORT. If the program hasn't returned the control it could be done from the console by the operator writing

100000 F
20000 F

Message append interprets the data in WPAN and appends it to the end of the character buffer. If the buffer is rotating, the characters will pan across the display in a readable pace. If it is stopped only the last four characters are shown. The buffer only takes 40 character, additional characters are ignored until next INIT or ABORT command.


The PAP has a real time calendar counting seconds and days. It is driven by the CPU's RT-clock oscillator and is powered by the standby power. The counters could be adjusted or read by programs via the four last commands to the PAP. When writing to the calendar, both counters are updated at the same time when the Write/Update high days command is executed. When reading the calendar the counters are sampled when the Read/Update low seconds command is executed.

The calendar is starting at zero at 00.00 January 1 1979 and will not overflow until 00.00 August 28 2068.