7.4.2. TX MAC Segmented Client Interface with Enabled Preamble Passthrough - When you turn on Preamble Passthrough in the parameter editor, you must provide 8 preamble bytes to the TX MAC segmented client interface.

When you turn on Preamble Passthrough in the parameter editor, you must provide 8 preamble bytes to the TX MAC segmented client interface.

The table below describes TX MAC segmented field positions with enabled Preamble Passthrough parameter.

MII Start of Packet control byte always replaces the first preamble byte.
Bits[55:8] are the preamble bits, typically set to the 0x55 value.
Bits[63:56] are the last preamble byte. In a standard preamble, it is set to the Start Frame Delimeter 0xD5 value.

Table 44. TX MAC Segmented Field Positions in `i_tx_mac_data` with Preamble Passthrough Enabled
Attention:
10GE/25GE requires multiple transfer cycle for header data.

The (') symbol in the **10GE/25GE i_tx_mac_data** column represents transfer on the subsequent cycle.

The ('') symbol in the **10GE/25GE i_tx_mac_data** column represents transfer on the 2^nd subsequent cycle.
100GE/400GE i_tx_mac_data	40GE/50GE i_tx_mac_data	10GE/25GE i_tx_mac_data	MAC Field	Note
[7:0]	[7:0]'	[7:0]''	Custom Preamble [7:0]	MII SOP control channel replaces it.
[15:8]	[15:8]'	[15:8]''	Custom Preamble [15:8]	0x55
[23:16]	[23:16]'	[23:16]''	Custom Preamble [23:16]	0x55
[31:24]	[31:24]'	[31:24]''	Custom Preamble [31:24]	0x55
[39:32]	[39:32]'	[39:32]''	Custom Preamble [39:32]	0x55
[47:40]	[47:40]'	[47:40]''	Custom Preamble [47:40]	0x55
[55:48]	[55:48]'	[55:48]''	Custom Preamble [55:48]	0x55
[63:56]	[63:56]'	[63:56]''	Custom Preamble [63:56]	0xD5 (SFD)
[71:64]	[71:64]'	[7:0]'	Dest Addr[47:40]
[79:72]	[79:72]'	[15:8]'	Dest Addr[39:32]
[87:80]	[87:80]'	[23:16]'	Dest Addr[31:24]
[95:88]	[95:88]'	[31:24]'	Dest Addr[23:16]
[103:96]	[103:96]'	[39:32]'	Dest Addr[15:8]
[111:104]	[111:104]'	[47:40]'	Dest Addr[7:0]
[119:112]	[119:112]'	[55:48]'	Src Addr[47:40]	When you turn on Source Address Insertion, contents are replaced by txmac_saddr unless `i_tx_skip_crc` is high.
[127:120]	[127:120]'	[63:56]'	Src Addr[39:32]
[135:128]	[7:0]	[7:0]	Src Addr[31:24]
[143:136]	[15:8]	[15:8]	Src Addr[23:16]
[151:144]	[23:16]	[23:16]	Src Addr[15:8]
[159:152]	[31:24]	[31:24]	Src Addr[7:0]
[167:160]	[39:32]	[39:32]	Length/Type[15:8]
[175:168]	[47:40]	[47:40]	Length/Type[7:0]
[…:176]	[127:48]	[63:48]	…

7.4.2. TX MAC Segmented Client Interface with Enabled Preamble Passthrough - When you turn on Preamble Passthrough in the parameter editor, you must provide 8 preamble bytes to the TX MAC segmented client interface. - 2026-01-06