Clicker; Keyboard Identification - IBM 5251 Series Maintenance Information Manual

Keyboard
The keyboard has three major parts: key modules, pad
printed circuit board, and logic printed circuit board.
Key modules, including the key tops, are the switches
the operator presses. A pad printed circuit board below
the key modules senses the pressed key by capacitive
coupling. The logic printed circuit board, which is
attached to the pad printed circuit board, contains the
scan counter; this converts th'e pressed key to a scan
code.
The scan code is loaded into an eight-position buffer on
the logic printed circuit board when the keyboard signals
the keyboard adapter control that a keystroke is ready to
be sent. A strobe pulse moves the keystroke scan code
to the keyboard adapter. The scan code moves through
the display station to the controller. The controller
interprets and converts the scan code to the appropriate
character indicated on the keyboard. The keyboard
identification specifies how the scan code is interpreted.
Typamatic keys load the character buffer with a scan
code for each scan code cycle. The typamatic key
operates at a rate of 10 to 15 repeated operations per
second (600 ms first cycle time).
The Shift and Shiftlock keys generate a break code
pulse. The break code tells the controller that there is a
change in shift status.
Clicker
A solenoid attached to the keyboard is activated after
the data has been sent from the logic printed circuit
board and has been stored by the MPU. The sound of
the solenoid is an aid to the operator because it
indicates that the next key may be pressed. Also, an
alarm function can be performed by this solenoid when
the keyboard adapter sends a series of pulses to the
solenoid.
Keyboard Identification
When requested, a 4-bit ID code is sent to the controller.
The ID code tells the controller which keyboard is being
used. The I D code is set up when pins are jumpered on
a plug board on the keyboard logic printed circuit board.
Theorv 5251 M 1M 4-5