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Intel
®
IXP45X and Intel
®
IXP46X Product Line of Network Processors—I2C Bus Interface Unit
Intel
®
IXP45X and Intel
®
IXP46X Product Line of Network Processors
Developer’s Manual
August 2006
896
Order Number: 306262-004US
Clear IDBR Receive Full bit to clear the interrupt.
Read IDBR data.
6. Read byte 2 with Nack (STOP is not set because STOP or Repeated START will be
decided on the byte read).
Write ICR: Clear START bit, Clear STOP bit, Enable Arb Loss interrupt, Set Ack/Nack
bit (Nack), Set Transfer Byte bit to initiate the access.
7. Wait for Buffer full interrupt.
Read status register: IDBR Receive Full (1), Unit Busy (1), R/W# bit (1), Ack/Nack
bit (1)
Clear IDBR Receive Full bit to clear the interrupt.
Read IDBR data.
There are now two options based on the byte read:
• Send a repeated START.
• Send a STOP only.
Here, a STOP abort is sent.
Note: Had a NACK not been sent, the next transaction must involve
another data byte read.
8. Send STOP abort condition. (STOP with no data transfer.)
Write ICR: Set Master abort.
21.8
Glitch Suppression Logic
The I
2
C Bus Interface Unit has built-in glitch suppression logic. Glitches will be
suppressed according to: 2 * (ICCR +1) * I
2
C clock period. For example, with a 33 MHz
(30-ns period) I
2
C clock, glitches of 60ns or less will be suppressed. This is within the
50-ns glitch suppression specification. Note, that for glitch suppression to be within
specification, it is required that (ICCR + 1) * I
2
C clock period > 25 ns. It is
recommended that (ICCR + 1) * I
2
C clock period = 30 ns.
21.9
Reset Conditions
Software is responsible for ensuring the I
2
C unit is not busy (ISR[3]) before asserting
reset. Software is also responsible for ensuring the I
2
C bus is idle when the unit is
enabled after reset. When directed to reset, the I
2
C unit returns to its default reset
condition.
When the Unit Reset bit in the ICR is set, only the I
2
C unit of the IXP45X/IXP46X
network processors resets and the associated I
2
C MMRs remain intact. When resetting
the I
2
C unit with the ICR’s unit reset, use the following guidelines:
1. In the ICR register, set the reset bit and clear the remainder of the register.
2. Clear the ISR register.
3. Clear reset in the ICR.
21.10
Register Definitions
The following registers are associated with the I
2
C Bus Interface Unit. They are all
located within the peripheral memory-mapped address space of the IXP45X/IXP46X
network processors.