NC 100/150/200 IO Specification

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This update to NCIOSPEC.TXT covers the differences between the NC100 hardware (documented in the original NCIOSPEC.TXT below) and the NC150/NC200 hardware.

This information was discovered mainly by Russell Marks during development of his NC emulator and ZCN software, with the remaining information found by myself during development of my NC200 emulation for M.E.S.S.

This update does not cover the NC150. I do not have details of any differences between this and the NC100 at this time.

When I have information on this system, it will be documented here.

These have been worked out by dissassembling the rom, and looking at patterns of I/O read/writes.

  • The NC200 does not have a TC8521 Real Time Clock, instead it has a MC146818 Real Time Clock. The MC146818 is no longer produced now, but is part of many PC designs.
  • The NC200 has a NEC765 compatible floppy disc controller. The disc interface was designed by Ranger Computers.

The ports listed in this section are different or have additional information to the NC100 port definitions. The other ports have the same function as the NC100.


  • The NC100 clock speed is 4.606MHz, at this time it is unknown if the NC200 has a different clock speed.
  • The NC100 on/off button generates an NMI.
  • The NC200 on/off button generates a maskable interrupt.

Keyboard NC100:

B0: 
bit 0: Shift (Left)
bit 1: Shift (Right)
bit 2: unused
bit 3: Cursor Left (Red)
bit 4: Return
bit 5: unused
bit 6: unused
bit 7: unused
B1:
bit 0: Function (Yellow)
bit 1: Control
bit 2: Stop
bit 3: Space
bit 4: unused
bit 5: unused
bit 6: 5
bit 7: unused

B2: 
bit 0: Caps Lock
bit 1: Symbol
bit 2: 1
bit 3: Tab
bit 4: unused
bit 5: unused
bit 6: unused
bit 7: unused
B3:
bit 0: 3
bit 1: 2
bit 2: Q
bit 3: W
bit 4: E
bit 5: unused
bit 6: S
bit 7: D
B4:
bit 0: 4
bit 1: unused
bit 2: Z
bit 3: X
bit 4: A
bit 5: unused
bit 6: R
bit 7: F

B5:
bit 0: B
bit 1: V
bit 2: T
bit 3: Y
bit 4: G
bit 5: C
B6:
bit 0: 6
bit 1: Cursor Down (Blue)
bit 2: Del
bit 3: Cursor Right (Green)
bit 4: \
bit 5: /
bit 6: H
bit 7: N
B7:
bit 0: =
bit 1: 7 
bit 2: ~
bit 3: Up
bit 4: Menu
bit 5: U
bit 6: M
bit 7: K
B8:
bit 0: 8
bit 1: -
bit 2: )
bit 3: (
bit 4: "
bit 5: I
bit 6: J
bit 7: ,
B9:
bit 0: 0
bit 1: 9
bit 2: Del
bit 3: P
bit 4: :
bit 5: L
bit 6: O
bit 7: STOP



Address                 Comment                 	R/W 
=======                 =======                 	===
00			Display Memory start		W
20			Memory card wait state		W
A0			Card Battery status		R
60			Interrupt Request Mask		W
70			on/off control			W		
80			Printer Status			R					
90			IRQ Status			R
B0-B9			Key data in			R
D0-D1			MC146818 Real Time Clock	R/W
E0	                NEC765 Status          		R
E1			NEC765 Data			R/W


Address = 00 Write only start address of display memory


bit 7           A15
bit 6           A14
bit 5           A13
bits 4-0        Not Used

Address = 20 Write only Memory card wait state control

bit 7: memory card wait state control:  1 for wait states, 0 for no wait
bit 0: NEC765 Terminal Count input (1=TC active, 0=TC inactive)

Address = 30 Write only Floppy motor control

bit 3: Floppy motor: 1=off, 0=on

Address = 70 on/off control


bit 2: Backlight: 1=off, 0=on
bit 0: on/off control: 1 = on, 0 = off


Address = 80 centronics status

bit 0: busy state

Address = A0 Card battery status


bit 7: memory card present 0 = yes, 1 = no
bit 6: memory card write protected 1 = yes, 0 = no
bit 5: lithium battery 0 if >= 2.7 volts
bit 4: input voltage = 1, if >= to 4 volts
bit 3: ** unknown use **
bit 2: alkaline batteries. 0 if >=3.2 volts
bit 1: ** unknown use **
bit 0: battery power: if 1: batteries are too low for disk usage, if 0: batteries ok for disc usage

Address = B0 - B9 Read only Keyboard data


B0..B9          each key of the 64 on the keyboard
                       will set a bit in one of these bytes
                       while pressed.

Russell Marks confirms that reading B9 does not clear the key scan interrupt like it does on the NC100. The interrupt must be explicitly cleared!

Address = 60 Write only Interrupt request mask


bit 7:		** unknown use **
bit 6: 		** unknown use ** (Real Time Clock Alarm?)
bit 5:		NEC765 FDC
bit 4:		Power off interrupt
bit 3           Key scan
bit 2           TC8251 Serial Interrupt (Tx Ready OR Rx Ready)
bit 1           ** unknown use ** (not checked by OS - not used?)
bit 0           ACK from parallel interface

Address = 80 Printer status

bit 7..1:	* unknown use *
bit 0:		printer busy status

1 = busy

Address = 90 Read/Write IRQ status


bit 7:		** unknown use **
bit 6: 		** unknown use ** (Real Time Clock Alarm?)
bit 5:		NEC765 FDC
bit 4:		Power off interrupt
bit 3           Key scan
bit 2           TC8251 Serial Interrupt (Tx Ready OR Rx Ready)
bit 1           ** unknown use ** (not checked by OS - not used?)
bit 0           ACK from parallel interface

Address = D0/D1 MC146818 Real Time Clock

Consult MC146818 datasheet.


Address = E0/E1 NEC765 floppy disc controller

Consult NEC765 datasheet.

Read:

E0 = Status, 
E1 = data

Write:

E0 = not used, 
E1 = data

Russell Marks's notes about sound generation on NC100

NC100 IO Specification