10 Mbps ARCNET (ANSI 878.1) Controller with 2Kx8 On-Chip RAM
Datasheet
ID bit, Excessive NAK bit, Reconfiguration Timer bit, and Transmitter Available bit. DMAEND bit is
inverted DMAEN bit on ADDRESS PTR High register. No other Status or Diagnostic Status bits can
generate an interrupt.
The six maskable status bits are ANDed with their respective mask bits, and the results are ORed to
produce the interrupt signal. An RI or TA interrupt is masked when the corresponding mask bit is reset to
logic "0", but will reappear when the corresponding mask bit is set to logic "1" again, unless the interrupt
status condition has been cleared by this time. A RECON interrupt is cleared when the "Clear Flags"
command is issued. An EXCNAK interrupt is cleared when the "POR Clear Flags" command is issued. A
New Next ID interrupt is cleared by reading the Next ID Register. If the DMAEND bit is not masked, the
interrupt occurs by finishing the DMA operation. The Interrupt Mask Register defaults to the value 0000
0000 upon hardware reset.
6.2.2 Data Register
This read/write 8-bit register is used as the channel through which the data to and from the RAM passes.
The data is placed in or retrieved from the address location presently specified by the address pointer.
The contents of the Data Register are undefined upon hardware reset. In case of READ operation, the
Data Register is loaded with the contents of COM20022I Internal Memory upon writing Address Pointer
low only once.
The SWAP bit is used to swap the upper and lower data byte. The SWAP bit is located at bit 0 of
ADDRESS PTR_LOW register. When 16 bit access is enabled, (W16=1), A0 becomes the SWAP bit.
6.2.3 Tentative ID Register
The Tentative ID Register is a read/write 8-bit register accessed when the Sub Address Bits are set up
accordingly (please refer to the Configuration Register and SUB ADR Register). The Tentative ID Register
can be used while the node is on-line to build a network map of those nodes existing on the network. It
minimizes the need for operator interaction with the network. The node determines the existence of other
nodes by placing a Node ID value in the Tentative ID Register and waiting to see if the Tentative ID bit of
the Diagnostic Status Register gets set. The network map developed by this method is only valid for a
short period of time, since nodes may join or depart from the network at any time. When using the
Tentative ID feature, a node cannot detect the existence of the next logical node to which it passes the
token. The Next ID Register will hold the ID value of that node. The Tentative ID Register defaults to the
value 0000 0000 upon hardware reset only.
6.2.4 Node ID Register
The Node ID Register is a read/write 8-bit register accessed when the Sub Address Bits are set up
accordingly (please refer to the Configuration Register and SUB ADR Register). The Node ID Register
contains the unique value which identifies this particular node. Each node on the network must have a
unique Node ID value at all times. The Duplicate ID bit of the Diagnostic Status Register helps the user
find a unique Node ID. Refer to the Initialization Sequence section for further detail on the use of the
DUPID bit. The core of the COM20022I does not wake up until a Node ID other than zero is written into
the Node ID Register. During this time, no microcode is executed, no tokens are passed by this node, and
no reconfigurations are caused by this node. Once a non-zero NodeID is placed into the Node ID
Register, the core wakes up but will not join the network until the TXEN bit of the Configuration Register is
set. While the Transmitter is disabled, the Receiver portion of the device is still functional and will provide
the user with useful information about the network. The Node ID Register defaults to the value 0000 0000
upon hardware reset only.
SMSC COM20022I
Page 33
Revision 09-27-07
DATASHEET
SMSC [ SMSC CORPORATION ]
