PIC18F97J60_11 Datasheet, PDF (249/492 Pages) Microchip Technology – 64/80/100-Pin, High-Performance, 1-Mbit Flash Microcontrollers with Ethernet

PIC18F97J60 FAMILY
19.5.2 TRANSMITTING PACKETS
The Ethernet module’s MAC will automatically
generate the preamble and Start-of-Frame (SOF)
delimiter fields when transmitting. Additionally, the
MAC can generate any padding (if needed) and the
CRC if configured to do so. The application must
generate and write all other frame fields into the buffer
memory for transmission.
In addition, the Ethernet module requires a single
per-packet control byte to precede the packet for trans-
mission. The control byte is organized as shown in
Figure 19-9. Before transmitting packets, the MAC
registers, which alter the transmission characteristics,
should be initialized as documented in Section 19.4
“Module Initialization”.
FIGURE 19-9:
FORMAT FOR PER-PACKET CONTROL BYTES
—
bit 7
bit 7-4
bit 3
bit 2
bit 1
bit 0
—
—
—
PHUGEEN PPADN PCRCEN POVERRIDE
bit 0
Unimplemented: Read as ‘0’
PHUGEEN: Per-Packet Huge Frame Enable bit
When POVERRIDE = 1:
1 = The packet will be transmitted in whole
0 = The MAC will transmit up to the number of bytes specified by the MAMXFL registers. If the packet
is larger than the bytes specified, it will be aborted after the MAMXFL registers specification is
reached.
When POVERRIDE = 0:
This bit is ignored.
PPADN: Per-Packet Padding Enable bit
When POVERRIDE = 1:
1 = The packet will be zero-padded to 60 bytes if it is less than 60 bytes
0 = The packet will be transmitted without adding any padding bytes
When POVERRIDE = 0:
This bit is ignored.
PCRCEN: Per-Packet CRC Enable bit
When POVERRIDE = 1:
1 = A valid CRC will be calculated and attached to the frame
0 = No CRC will be appended. The last 4 bytes of the frame will be checked for validity as a CRC.
When POVERRIDE = 0:
This bit is ignored.
POVERRIDE: Per-Packet Override bit
1 = The values of PCRCEN, PPADN and PHUGEEN will override the configuration defined by
MACON3
0 = The values in MACON3 will be used to determine how the packet will be transmitted
 2011 Microchip Technology Inc.
DS39762F-page 249