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STP2002QFP
Sun Microelectronics
Fast Ethernet, Parallel Port, SCSI (FEPS) - STP2002QFP
Note: To ensure proper operation of the TX_MAC, the TX_MAC_En
bit must always be cleared to 0 and a delay imposed before a PIO write
to any of the other bits in the TX_MAC Configuration register or any
of the MAC parameters registers is performed. The MAC parameters’
registers are IPG1, IPG2, AttemptLimit, SlotTime, PA_Size,
PA_Pattern, SFD_Pattern, JamSize, TxMinFrameSize, and TxMax-
FrameSize.
The amount of delay required will depend on the time required to trans-
mit a maximum size frame, and is thus dependent on the value
programmed into the TxMaxFrameSize register and the data rate on
the medium. For a standard 1518-byte frame on a 100-Mbps network,
the delay would be 125 msec. To avoid the requirement for a variable
time delay, the TX_MAC_En bit may be polled, and when this bit
reads back as a 0, all the registers mentioned above may be written,
including all the other bits in the configuration register.
7.5.31 TX_MAC InterPacketGap1 RegisterThis eight-bit register defines the first 2/3 portion of the InterPacketGap,
which is timed by the TX_MAC before each frame’s transmission is initiated.
For back-to-back transmissions, this value is added to the value in the
InterPacketGap2 register, and during the entire period the CarrierSense input
signal is ignored by the TX_MAC. For a reception followed by a transmis-
sion, the TX_MAC will monitor the CarrierSense input signal during the time
interval specified in this register and will respond to it, but will ignore it dur-
ing the time interval specified in the InterPacketGap2 register. The time in-
terval specified in this register is in units of media byte time.
Default value: 0x08.
Table 145: TX_MAC InterPacketGap1 Register Address
Register Physical Address Access Size
InterPacketGap1 register 0x8C0_6210 4 bytes
Table 146: TX_MAC InterPacketGap1 Register Definition
Field Bits Description Type
7:0 First 2/3 portion of IPG, timed by TX_MAC
before frame transmission in initiated
R/W