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EMAC Port Registers
5.46 Transmit Channel 
The transmit channel 
Figure 74. Transmit Channel n DMA Head Descriptor Pointer Register (TXnHDP)
31  | 16  | 
  | TXnHDP | 
  | |
15  | 0  | 
TXnHDP
LEGEND: R/W = Read/Write; 
Table 74. Transmit Channel n DMA Head Descriptor Pointer Register (TXnHDP) Field Descriptions
Bit | Field  | Value Description  | 
TXnHDP  | Transmit channel n DMA Head Descriptor pointer. Writing a transmit DMA buffer descriptor address  | |
  | 
  | to a head pointer location initiates transmit DMA operations in the queue for the selected channel.  | 
  | 
  | Writing to these locations when they are nonzero is an error (except at reset). Host software must  | 
  | 
  | initialize these locations to zero on reset.  | 
132  | Ethernet Media Access Controller (EMAC)/Management Data Input/Output (MDIO)  | SPRU975B   |