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5.2.2 Outline of the Shadow Block Register
Each transport layer in the host system and device has a block register, which is
called a Shadow Block Register in the host system, and a Block Register in the
device.
These registers are used when the host system issues a command to the device.
Table 5.4 Shadow Block Register
Command Block registers
Read Write
Data Port
Error Features
Sector Count (exp) Sector Count Sector Count (exp) Sector Count
Sector Number (exp) Sector Number Sector Number (exp) Sector Number
Cylinder Low (exp) Cylinder Low Cylinder Low (exp) Cylinder Low
Cylinder High (exp) Cylinder High Cylinder High (exp) Cylinder High
Device / Head
Status Command
Control Block registers
Alternate Status Device Control
Note: Each of the Sector Count, Sector Number, Cylinder Low, and Cylinder
High fields has a higher-order field used for issuing the Ext command.
The fields are called Sector Count exp, Sector Number exp, Cylinder
Low exp, and Cylinder High exp, respectively. For information on
writing data to these fields, see "Device Control Field."
5-16 C141-E249