Functions Performed At Power-On Time; Power-On Reset; Basic Assurance Test - IBM 5170 Technical Reference

keyboard controller. When the key is released, its break code is
sent (the break code for a key is its make code preceded by hex
FO).
All keys are tyPematic. When a key is pressed and held down, the
keyboard continues to send the make code for that key until the
key is released. The rate at which the make code is sent is known
as the typematic rate (The typematic rate is described under "Set
Typematic Rate/Delay"). When two or more keys are held
down, only the last key pressed repeats at the typematic rate.
Typematic operation stops when the last key pressed is released,
even if other keys are still held down. When a key is pressed and
held down while the interface is inhibited, only the first make
code is stored in the buffer. This prevents buffer overflow as a
result of typematic action.
Functions Performed at Power-On Time
Power-On Reset
The keyboard logic generates a POR when power is applied to the
keyboard. The POR lasts a minimum of 300 milliseconds and a
maximum of 9 seconds.
Note: The keyboard may issue a false return during the first
200 milliseconds after the +5 Vdc is established at the 90%
level. Therefore, the keyboard interface is disabled for this
period.
Basic Assurance Test
Immediately following the POR, the keyboard executes a basic
assurance test (BAT). This test consists of a checksum of all
~
read-only memory (ROM), and a stuck-bit and addressing test of
all random-access memory (RAM) in the keyboard's
microprocessor. The mode indicators-three light emitting diodes
4-4 Keyboard