Inter-Byte Clocking

UltraScale Architecture SelectIO Resources User Guide (UG571)

Document ID
UG571
Release Date
2022-08-31
Revision
1.14 English

Inter-byte clocking allows clock sharing between a clock arriving at a BITSLICE_0 of one nibble and the nibbles in the same position of other bytes (This Figure). Sharing of the input or sample clock is done through CLK_TO_EXT_NORTH(SOUTH) output pins and CLK_FROM_EXT input pins in BITSLICE_CONTROL components of other bytes. Inter-byte clocking is started by setting attributes EN_CLK_TO_EXT_NORTH(SOUTH).

Figure 2-69:      Inter-Byte Clocking

X-Ref Target - Figure 2-69

X16053-inter-byte-clocking.jpg

Note:   This Figure and This Figure do not show BITSLICE_6 of the upper nibble.

Inter-nibble and inter-byte clocking can be combined to serve all bit slices in an I/O bank with the same clock (see This Figure).

Figure 2-70:      Combination of Inter-Nibble and Inter-Byte Clocking

X-Ref Target - Figure 2-70

X16054-combination-of-inter-nibble-and-inter-byte-clocking.jpg

Notes on This Figure.

Assume that byte_2, lower nibble, RX_BITSLICE_0 is set up as a clock or strobe input.

Byte_2, upper nibble must be inter-nibble clock-enabled.

Because the lower nibble of byte_2 is used as clock input, and all nibbles are used in multi-byte setup, for all bytes the lower nibble must supply the clock to the upper nibble for inter-nibble clocking.

Byte_3, lower nibble, gets a clock from the CLK_TO_EXT_NORTH output of the lower nibble of byte 2 on its CLK_FROM_EXT input.

The lower byte south (down) of byte_2, lower nibble supplies a clock from the CLK_TO_EXT_SOUTH output to the CLK_FROM_EXT input of the lower nibble of byte 1.

To reach the lower nibble of byte 0, the CLK_TO_EXT_SOUTH output of byte 1 must be connected to the CLK_FROM_EXT input of the lower nibble of byte 0. A jump over is made inside byte 1 between the CLK_FROM_EXT and CLK_TO_EXT_SOUTH pins. As such, all receivers in all nibbles are configured to receive data from a forwarded version (via inter-byte/nibble) of the strobe sourced from the byte_2 upper nibble.

The attribute setups for this example are listed in Table: Attributes for Inter-Byte Clocking Example  and Table: Enabling Inter-Nibble Clocking.

Table 2-33:      Attributes for Inter-Byte Clocking Example 

Byte

Attribute

Type

Byte 3

EN_CLK_TO_EXT_NORTH

DISABLE

EN_CLK_TO_EXT_SOUTH

DISABLE

Byte 2

EN_CLK_TO_EXT_NORTH

ENABLE

EN_CLK_TO_EXT_SOUTH

ENABLE

Byte 1

EN_CLK_TO_EXT_NORTH

DISABLE

EN_CLK_TO_EXT_SOUTH

ENABLE

Byte 0

EN_CLK_TO_EXT_NORTH

DISABLE

EN_CLK_TO_EXT_SOUTH

DISABLE

Notes:

1.Unused CLK_FROM_EXT pins must be tied High.

For all nibbles, inter-nibble clocking must be enabled as listed in Table: Enabling Inter-Nibble Clocking.

Table 2-34:      Enabling Inter-Nibble Clocking

Nibble

Attribute

Type

Upper Nibble

EN_OTHER_NCLK

TRUE

EN_OTHER_PCLK

TRUE

Lower Nibble

EN_OTHER_NCLK

FALSE

EN_OTHER_PCLK

FALSE