Read Device Characteristics - IBM Multiprise 3000 Reference Manual

Read Device Characteristics

Description: The Read Device Characteristics command transfers 64 bytes to the
channel.
The information this command transfers defines the characteristics of the
addressed logical volume. The ECKD architecture states that the characteristics of
the emulated device rather than those of the physical device are returned, except
for Bytes 56 and 57 which pertain to the real control unit and device. See
Appendix A, "Device Characteristics" on page A-1 for the specific values. This
command resets track orientation in the control unit.
If the device has never been available to the subsystems, the device model cannot
be determined. In this case the device type and model will be X'00' and all model
dependent data will be zeros (bytes 2–5, 12–13, 28–29, 32–33, 36–41).
Chaining and Restrictions: If this command is in a Locate Record or Locate
Record Extended domain, it is rejected with unit check status. The sense data
contains command reject with format 0, message 2.
See "Effect of Subsystem and Device State on Status Presented to Command" on
page 2-5 for the operation of this command when other subsystem and device
status conditions occur.
Device Characteristics Information
The device characteristics data format follows. The first six bytes are the same as
bytes 1 through 6 of the Sense ID command. See Appendix A, "Device
Characteristics" on page A-1 for the values of bytes 0 through 63.
4-54
Internal Disk Subsystem Reference Guide
Hex Code Data Address
64 The main storage location for the first byte of device
characteristics information.
Count
64