Word Format

Versal ACAP Technical Reference Manual (AM011)

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1.4 English

The word format is designed to closely manage the flow of RX and TX data. Receive data is always via the RXFIFO. Transmit data can be written via the 32-bit TXFIFO or the 8-bit immediate data field in the command word.

Software writes the controller commands to the Cmd_FIFO_Data register. They are buffered in the 32-word deep command FIFO. The command word fields are described in the following table.

Table 1. Controller Command Word Format
Field Name Bits Description
[IMM_DATA] 7:0

Multipurpose field for data or byte count


Select [IMM_DATA] field usage:
0: Immediate write data RXFIFO
1: Data byte count in the format defined by [EXP]; write data is sent via the TXD data port

Note: Read data is always received via the RXD data port (RXFIFO).
[EXP] 9

Select byte count calculation method:
0: Absolute count is in [IMM_DATA] field (maximum of 256 bytes)
1: Exponential count is calculated as byte transfer count = 2 ^ [IMM_DATA]

[MODE] 11:10

00: Reserved, do not use
01: 1-bit data I/O
10: 2-bit data I/O
11: 4-bit data I/O


Lower chip select control:
0: Deassert
1: Assert


Upper chip select control:
0: Deassert
1: Assert

[BUS_SEL] 15:14

Data bus enables for clocking:
00: No bus
01: Lower bus only
10: Upper bus only
11: Both buses
Bus width depends on [MODE]

[TX] 16

Transmit data enable:
0: Disable
1: Send data (immediate or via TXFIFO)

[RX] 17

Receive data enable:
0: Disable
1: Receive data (via RXFIFO)


Data stripe enable:
0: Disable (same data appears on upper and lower buses)
1: Enable (data is striped across lower and upper buses)

[POLL] 19

RX data polling enable
0: Disable
1: Enable