IBM Z9 Planning Manual page 53

register exists for each CPU and contains the TOD programmable field in bits
16-31. The TOD programmable register is set by a new privileged instruction, SET
TOD PROGRAMMABLE FIELD (SCKPF). The leftmost byte of the extended form
TOD clock is the TOD Epoch Index (TEX), and is stored as zeros in machines
running ESA/390.
The extended TOD clock facility satisfies three main objectives:
v Relieve constraints that exist in the current 64-bit TOD clock
v Extend the TOD-clock architecture to multi-system configurations
v Help ensure sysplex-wide uniqueness of the STCKE TOD values
The TOD Programmable Field (TODPF) is a 16-bit quantity contained in bit
positions 16-31 of the TOD programmable register. The contents of the register can
be set by the privileged instruction SET TOD PROGRAMMABLE FIELD. The
contents of the register can be stored by the instruction STORE CLOCK
EXTENDED, which stores the TOD programmable field in the last 16 bits of the
extended form TOD clock. The contents of the register are reset to a value of all
zeros by an initial CPU reset.
1-27
Chapter 1. Introduction to Logical Partitions