Editing Psion Organiser II (section)

=== Keyboard ===

The '''AC''' key (top left) is special: it is wired straight to the control IC and to port 5 bit 7, and it is what switches the machine on. The other '''35 keys form a 7 × 5 matrix'''. The seven outputs K1–K7 are open-drain and are pulled low one at a time; the processor reads KBD1–KBD5 on port 5 bits 2–6, and a low means a key is down. The switches are '''PCB pads under the keys, shorted by a conductive rubber pad'''.<ref name="tech2" />

The K1–K7 outputs are not a dedicated peripheral — they are '''bits 1–7 of the second stage of the real-time clock divider chain''', which is why the keyboard can only be polled when the NMI latch is set to interrupt the processor directly.<ref name="tech2" />

The Technical Manual's published key matrix is reproduced below. '''Note that as printed it contains three apparent duplicates (G, S and Y) and omits E and T''', so it should be verified against a real machine before being relied on:<ref name="tech2" />

{| class="wikitable styled-table" style="width:75%; text-align:center;"
|+'''Keyboard matrix as published'''<ref name="tech2" />
! !! KBD5 !! KBD4 !! KBD3 !! KBD2 !! KBD1
|-
! Port 5 bit
| 6 || 5 || 4 || 3 || 2
|-
! K7
| D || J || P || V || S
|-
! K6
| F || L || R || X || EXE
|-
! K5
| G || K || Q || W || DEL
|-
! K4
| C || I || O || U || Z
|-
! K3
| B || H || N || Y || Y
|-
! K2
| A || G || M || S || SH
|-
! K1
| RA || LA || DA || UA || MODE
|}

Even with those errors, the structure is what matters for repair: '''a dead row is one K output, a dead column is one KBD input.'''