10 Mbps ARCNET (ANSI 878.1) Controller with 2Kx8 On-Board RAM
Datasheet
TRI bit and the interrupt. It is not necessary, however, to clear the bit or the interrupt right away because
the status of the receive operation is double buffered in order to retain the results of the first reception for
analysis by the processor, therefore the information will remain in the Status Register until the "Clear
Receive Interrupt" command is issued. Note that the interrupt will remain active until the "Clear Receive
Interrupt" command is issued, and the second interrupt will be stored until the first interrupt is
acknowledged. A minimum of 200nS (at EF=1) interrupt inactive time interval between interrupts is
guaranteed.
The second reception will occur as soon as a second packet is sent to the node, as long as the second
"Enable Receive to Page fnn" command was issued. The operation is as if a new "Enable Receive to
Page fnn" command has just been issued. After the first Receive status bits are cleared, the Status
Register will again be updated with the results of the second reception and a second interrupt resulting
from the second reception will occur.
In the COM20022I 3V, the Receive Inhibit (RI) bit of the Interrupt Mask Register now masks only the TRI
bit of the Status Register, not the RI bit as in the non-chaining mode. Since the TRI bit is only set upon
reception of a packet (not by RESET), and since the TRI bit may easily be reset by issuing a "Clear
Receive Interrupt" command, there is no need to use the RI bit of the Interrupt Mask Register to mask
interrupts generated by the TRI bit of the Status Register. In Command Chaining mode, the "Disable
Receiver" command will cancel the oldest reception, unless the reception has already begun. If both
receptions should be canceled, two "Disable Receiver" commands should be issued.
6.4.3 Reset Details
6.4.3.1 Internal Reset Logic
The COM20022I 3V includes special reset circuitry to guarantee smooth operation during reset. Special
care is taken to assure proper operation in a variety of systems and modes of operation. The COM20022I
3V contains digital filter circuitry and a Schmitt Trigger on the nRESET signal to reject glitches in order to
ensure fault-free operation.
The COM20022I 3V supports two reset options; software and hardware reset. A software reset is
generated when a logic "1" is written to bit 7 of the Configuration Register. The device remains in reset as
long as this bit is set. The software reset does not affect the microcontroller
interface
modes
determined after hardware reset, nor does it affect the contents of the Address Pointer Registers, the
Configuration Register, or the Setup1 Register. A hardware reset occurs when a low signal is asserted on
the nRESET input. The minimum reset pulse width is 5TXTL. This pulse width is used by the internal digital
filter, which filters short glitches to allow only valid resets to occur
Upon reset, the transmitter portion of the device is disabled and the internal registers assume those states
outlined in the Internal Registers section. After the nRESET signal is removed the user may write to the
internal registers. Since writing a non-zero value to the Node ID Register wakes up the COM20022I 3V
core, the Setup1 Register should be written before the Node ID Register. Once the Node ID Register is
written to, the COM20022I 3V reads the value and executes two write cycles to the RAM buffer. Address 0
is written with the data D1H and address 1 is written with the Node ID. The data pattern D1H was chosen
arbitrarily, and is meant to provide assurance of proper microsequencer operation.
6.5
Initialization Sequence
6.5.1 Bus Determination
Writing to and reading from an odd address location from the COM20022I 3V's address space causes the
COM20022I 3V to determine the appropriate bus interface. When the COM20022I 3V is powered on the
SMSC COM20022I 3V
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Revision 02-27-06
DATASHEET
SMSC [ SMSC CORPORATION ]
