
PRS28.4G
IBM Packet Routing Switch
prs28.03.fm
August 31, 2000
Internal Registers
Page 57 of 131
5.2.1 Indirect Access of Memory Data and Look-Up Table
5.2.1.1 Shared Memory Access
The internal shared packet memory can be accessed (for testing or to receive/transmit Control Packets) via
the Memory Row Data Register, an internal 20-byte register. This register, together with the Memory Row
Address Register and specific Row Read and Write commands in the Command Register, allow reading and
writing of any location in the shared memory.
To Write to a Specific Row in the Shared Memory:
1. Specify the row address and select the bank (master or slave) in the Memory Row Address Register.
2. Build the data to be written in the Memory Row Data register via the Table Pointer and Table Data regis-
ters.
a. Set the Table Pointer register to ‘0’b
b. Write two data bytes to the Table Data register. After each write, the Table Pointer register is
automatically incremented by two.
c. Repeat (b) until the desired row is built.
3. Trigger a Row Write Command via the Command Register.
To Read a Specific Row from the Shared Memory:
1. Specify the row address and select the bank (master or slave) in the Memory Row Address Register.
2. Trigger a Row Read Command via the Command Register.
3. Read the data from the Memory Row Data register via the Table Pointer and Table Data registers. Note
that if the processor tries to read the Memory Row Data register before the data is available, a Processor
Error interrupt will be asserted. To read the Memory Row Data register:
a. Set the Table Pointer register to ‘0’b.
b. Read two data bytes to the Table Data register. After each read, the Table Pointer register is
automatically incremented by two.
c. Repeat (b) until the desired row is read.
5.2.1.2 Look-Up Table Access
The lookup tables are accessed via the Table Pointer and Data registers in the same manner as the Memory
Row Data register (see the two subsections above). Use the Table Select bit of the Table Pointer register to
select between the Look-Up tables and the Memory Row Data Register.
5.2.2 Register Formats
The following section describes each of the individual application registers accessible through the OCM inter-
face. These registers are used to provide initialization, programmability and status monitoring of the device.
Upon a reset, all application registers are initialized to ‘0’, except as noted in the individual register descrip-
tions.