IBM 5170 Technical Reference page 61

empty. A 1 indicates that data has been written into the
buffer but the controller has not read the data. When the
controller reads the input buffer, this bit will return to O.
Bit 2 System Flag-This bit may be set to 0 or 1 by writing to
the system's flag bit in the keyboard controller's
command byte. It is set to 0 after a power on reset.
Bit 3
Command/Data-The keyboard controller's input buffer
may be addressed as either I/O address hex 60 or 64.
Address hex 60 is defined as the data port, and address
hex 64 is defined as the command port. Writing to
address hex 64 sets this bit to 1; writing to address hex 60
sets this bit to O. The controller uses this bit to determine
if the byte in its input buffer should be interpreted as a
command byte or a data byte.
Bit 4
Inhibit Switch-This bit is updated whenever data is
placed in the keyboard controller's output buffer. It
reflects the state of the keyboard-inhibit switch. A 0
indicates the keyboard is inhibited.
~,
Bit 5
Transmit Time-Out-A 1 indicates that a transmission
started by the keyboard controller was not properly
completed.
If
the transmit byte was not clocked out
within the specified time limit, this will be the only error.
If
the transmit byte was clocked out but a response was
not received within the programmed time limit, the
transmit time-out and receive time-out error bits are set
On. If the transmit byte was clocked out but the response
was received with a parity error, the transmit time-out
and parity error bits are set On.
Bit 6 Receive Time-Out-A 1 indicates that a transmission was
started by the keyboard but did not finish within the
programmed receive time-out delay.
Bit 7 Parity Error-A 0 indicates the last byte of data received
from the keyboard had odd parity. A 1 indicates the last
byte had even parity. The keyboard should send with odd
parity.
System Board 1-39