Keyboard Outputs; Key Scan Codes - IBM 5170 Technical Reference

Keyboard Outputs
Key Scan Codes
Each key is assigned a unique 8-bit, make, scan code, which is
sent when the key is pressed. Each key also sends a break code
when the key is released. The break code consists of two bytes,
the first of which is the break code prefix, hex FO; the second
byte is the same as the make scan code for that key.
The typematic scan code for a key is the same as the key's make
code. The following figure is a keyboard layout.
4-10 Keyboard