Datasheet

ENC424J600/624J600
DS39935C-page 80  2010 Microchip Technology Inc.
REGISTER 8-3: MACON2: MAC CONTROL REGISTER 2
U-0 R/W-1 R/W-0 R/W-0 U-0 U-0 R/W-0 R/W-0
— DEFER BPEN NOBKOFF — — r r
bit 15 bit 8
R/W-1 R/W-0 R/W-1 R/W-1 R/W-0 R/W-0 R/W-1 R/W-0
PADCFG2 PADCFG1 PADCFG0 TXCRCEN PHDREN HFRMEN
r FULDPX
bit 7 bit 0
Legend:
R = Readable bit W = Writable bit U = Unimplemented bit, read as ‘0’
-n = Value at POR ‘1’ = Bit is set ‘0’ = Bit is cleared x = Bit is unknown
bit 15
Unimplemented: Read as ‘0’
bit 14
DEFER: Defer Transmission Enable bit (applies to half duplex only)
1 = When the medium is occupied, the MAC will wait indefinitely for it to become free when attempting
to transmit (use this setting for IEEE 802.3 compliance)
0 = When the medium is occupied, the MAC will abort the transmission after the excessive deferral
limit is reached (24,288 bit times)
bit 13
BPEN: No Backoff During Back Pressure Enable bit (applies to half duplex only)
1 = After incidentally causing a collision during back pressure, the MAC immediately begins retransmitting
0 = After incidentally causing a collision during backpressure, the MAC delays using the binary
exponential backoff algorithm before attempting to retransmit (normal operation)
bit 12
NOBKOFF: No Backoff Enable bit (applies to half duplex only)
1 = After any collision, the MAC immediately begins retransmitting
0 = After any collision, the MAC delays using the binary exponential backoff algorithm before
attempting to retransmit (normal operation)
bit 11-10
Unimplemented: Read as ‘0’
bit 9-8
Reserved: Write as ‘0’
bit 7-5
PADCFG<2:0>: Automatic Pad and CRC Configuration bits
111 = All short frames are zero-padded to 64 bytes and a valid CRC is then appended
110 = No automatic padding of short frames
101 = MAC automatically detects VLAN protocol frames which have a 8100h type field and auto-
matically pad to 64 bytes. If the frame is not a VLAN frame, it will be padded to 60 bytes. After
padding, a valid CRC is appended.
100 = No automatic padding of short frames
011 = All short frames are zero-padded to 64 bytes and a valid CRC is then appended
010 = No automatic padding of short frames
001 = All short frames will be zero-padded to 60 bytes and a valid CRC is then appended
000 = No automatic padding of short frames
bit 4
TXCRCEN: Transmit CRC Enable bit
1 = MAC appends a valid CRC to all frames transmitted regardless of the PADCFG bits. TXCRCEN
must be set if the PADCFG bits specify that a valid CRC will be appended.
0 = MAC does not append a CRC. The last 4 bytes are checked and if it is an invalid CRC, it is to be
reported by setting CRCBAD (ETXSTAT<4>).
bit 3
PHDREN: Proprietary Header Enable bit
1 = Frames presented to the MAC contain a 4-byte proprietary header which is not used when
calculating the CRC
0 = No proprietary header is present; the CRC covers all data (normal operation)