NEC LS2400 User Manual page 146

For example, a test point error code of 16 is indicated by a
1-2-2-3 beep code (a single beep, a burst of two beeps, a
burst of two beeps, and a burst of three beeps). In addition,
BIOS writes a value of 16 on the upper left corner of the
display screen and to I/O port 80h to enable debugging
tools to identify the area of failure.
The "POST Tests" table is a list of the test point error codes
written at the start of each POST test and the beep codes
issued for terminal errors.
Problem Solving 5-29