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C141-E034-02EN 5 - 37
(16) EXECUTE DEVICE DIAGNOSTIC (X'90')
This command performs an internal diagnostic test (self-diagnosis) of the device. This command
usually sets the DRV bit of the Drive/Head register is to 0 (however, the DV bit is not checked). If
two devices are present, both devices execute self-diagnosis.
If device 1 is present:
• Both devices shall execute self-diagnosis.
• The device 0 waits for up to 5 seconds until device 1 asserts the PDIAG- signal.
• If the device 1 does not assert the PDIAG- signal but indicates an error, the device 0 shall
append X‘80’ to its own diagnostic status.
• The device 0 clears the BSY bit of the Status register and generates an interrupt. (The device
1 does not generate an interrupt.)
• A diagnostic status of the device 1 is read by the host system. When a diagnostic failure of the
device 1 is detected, the host system can read a status of the device 1 by setting the DV bit
(selecting the device 1).
When device 1 is not present:
• The device 0 posts only the results of its own self-diagnosis.
• The device 0 clears the BSY bit of the Status register, and generates an interrupt.
Table 5.6 lists the diagnostic code written in the Error register which is 8-bit code.
If the device 1 fails the self-diagnosis, the device 0 "ORs" X‘80’ with its own status and sets that
code to the Error register.
Table 5.6 Diagnostic code
Code Result of diagnostic
X‘01’
X‘03’
X‘05’
X‘8x’
No error detected.
Data buffer compare error
ROM sum check error
Failure of device 1