Compaq EV68A specifications Cbox Data Register Cdata, Cbox Shift Register Cshft

Cbox CSRs and IPRs

5.4.1 Cbox Data Register – C_DATA

Figure 5–35shows the Cbox data register.

Figure 5–35 Cbox Data Register

636 50

C_DATA[5:0]

			LK99-0043A
	Table 5–22describes the Cbox data register fields.
Table 5–22 Cbox Data Register Fields Description
Name	Extent	Type	Description
Reserved	[63:6]	—	—
C_DATA[5:0]	[5:0]	RW	Cbox data register. A HW_MTPR instruction to this register causes six
			bits of data to be placed into a serial shift register. When the
			HW_MTPR instruction is retired, the data is shifted into the Cbox. After
			the Cbox shift register has been accessed, performing a HW_MFPR
			instruction to this register will return six bits of data.

5.4.2 Cbox Shift Register – C_SHFT

Figure 5–36shows the Cbox shift register.

Figure 5–36 Cbox Shift Register

631 0

C_SHIFT

			LK99-0044A
	Table 5–23describes the Cbox shift register fields.
Table 5–23 Cbox Shift Register Fields Description
Name	Extent	Type	Description
Reserved	[63:1]	—	—
C_SHIFT	[0]	W1	Writing a 1 to this register bit causes six bits of Cbox IPR data to shift into
			the Cbox data register. Software can then use a HW_MFPR read operation
			to the Cbox data register to read the six bits of data.

5.4.3 Cbox WRITE_ONCE Chain Description

The WRITE_ONCE chain order is contained in Table 5–24.In the table:

•Many CSRs are duplicated for ease of hardware implementation. These CSRs are indicated in italics. They must be written with values that are identical to the values written to the original CSRs.

21264/EV68A Hardware Reference Manual Internal Processor Registers 5–33