3.6.7 Data Blocking Register

This register is used to send data via the TxEngine and receive data from the RxEngine.

The DBR characteristics are:

Usage constraints
Upper bytes must be the NULL flag (0xAF) on writes.
Available in all SDC-600 configurations.
32-bit read/write memory-mapped register located at offset 0x30.

The DR and DBR operate identically, except on writes where more data is written to the TxEngine than the COM Port can accept. In this case:

  • When writing to the DR, the write access completes with an OK response and an overflow error is logged in SR.TXOE.
  • When writing to the DBR, the write access stalls until there is sufficient space.

The following figure shows the bit assignments.

Figure 3-12 DBR bit assignments
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The following table shows the bit assignments.

Table 3-13 DBR bit assignments

Bits Name Function
[31:0] DATA

Data transfer. Only 32-bit access size is supported to DBR.

On writes:

  • Transfers the lowest byte into the TxEngine FIFO for transmission.
  • The upper bytes must be written with the NULL Flag byte value.
  • The TxEngine ignores the NULL Flag byte value.
  • If TxEngine FIFO is not empty and the byte to be transmitted to the TxEngine is not a NULL Flag byte, the write to the DBR stalls until the FIFO empties.
  • If SR.TXOE or SR.TXLE is 1, then writes are ignored.
  • If SR.TXLE is 1, then writes are ignored and any outstanding write access is terminated with an OK response.

On reads:

  • Returns one byte from the RxEngine FIFO at the lowest byte.
  • If the RxEngine FIFO is empty, the lowest byte returns the NULL Flag byte. The upper bytes always return the NULL Flag byte.
  • Read accesses complete immediately.
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