82596DX Datasheet, PDF (31/77 Pages) Intel Corporation – HIGH-PERFORMANCE 32-BIT LOCAL AREA NETWORK COPROCESSOR

82596DX SX
 Operation of the Bus Throttle The SCB controls the Bus Throttle timers by providing them with new values
and sending the Load and Start timer commands The timers can be operated in both the 32-bit Segmented
and Linear modes
 Reception of frames by the Receive Unit (RU) The SCB controls the RU by specifying the address of the
Receive Frame Area and by starting suspending resuming or aborting frame reception
 Acknowledgment of events that cause interrupts
 Resetting the chip
The 82596 sends status reports to the CPU via the System Control Block The SCB contains four types of
status reports
 The cause of the current interrupts These interrupts are caused by one or more of the following 82596
events
 The Command Unit completes an Action Command that has its I bit set
 The Receive Unit receives a frame
 The Command Unit becomes inactive
 The Receive Unit becomes not ready
 The status of the Command Unit
 The status of the Receive Unit
 Status reports from the 82596 regarding reception of corrupted frames
Events can be cleared only by CPU acknowledgment If some events are not acknowledged by the ACK field
the Interrupt signal (INT) will be reissued after Channel Attention (CA) is processed Furthermore if a new
event occurs while an interrupt is set the interrupt is temporarily cleared to trigger edge-triggered interrupt
controllers
The CPU uses the Channel Attention line to cause the 82596 to examine the SCB This signal is trailing-edge
triggered the 82596 latches CA on the trailing edge The latch is cleared by the 82596 before the SCB
control command is read
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ACK
ODD WORD
X CUC R RUC
RFA OFFSET
ALIGNMENT ERRORS
OVERRUN ERRORS
16 15
X X X X STAT
EVEN WORD
0 CUS 0 RUS
CBL OFFSET
CRC ERRORS
RESOURCE ERRORS
0
0 0 0 0 SCB
SCB a 4
SCB a 8
SCB a 12
Figure 18 SCB 82586 Mode
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ODD WORD
16 15
ACK 0 CUC R RUC 0 0 0 0 STAT 0
RFA OFFSET
CRC ERRORS
ALIGNMENT ERRORS
RESOURCE ERRORS ( )
OVERRUN ERRORS ( )
RCVCDT ERRORS ( )
SHORT FRAME ERRORS
T-ON TIMER
In MONITOR mode these counters change function
EVEN WORD
CUS
RUS
CBL OFFSET
T-OFF TIMER
Figure 19 SCB 32-Bit Segmented Mode
0
T 0 0 0 SCB
SCB a 4
SCB a 8
SCB a 12
SCB a 16
SCB a 20
SCB a 24
SCB a 28
SCB a 32
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