MU9C2481L Datasheet, PDF (6/20 Pages) MUSIC Semiconductors – LANCAM® 1ST Family

LANCAM 1^ST Family
OPERATIONAL CHARACTERISTICS Continued
THE REGISTER SET
The Control, Segment Control, Address, Mask Register 1,
and the Persistent Source and Destination registers are
duplicated, with one set termed the Foreground set, and
the other the Background set. The active set is chosen by
issuing Select Foreground Registers or Select Background
Registers instructions. By default, the Foreground set is
active after a reset. Having two alternate sets of registers
that determine the device configuration allows for a rapid
return to a foreground network filtering task from a
background housekeeping task.
Writing a value to the Control register or writing data to the
last segment of the Comparand or either mask register will
cause an automatic comparison to occur between the
contents of the Comparand register and the words in the
CAM segments of the memory marked valid, masked by
MR1 or MR2 if selected in the Control register.
Instruction Decoder
The Instruction decoder is the write-only decode logic for
instructions and is the default destination for Command
Write cycles. If an instruction’s Address Field flag (bit 11)
is set to a 1, it is a two-cycle instruction that is not executed
immediately. For the next cycle only, the data from a
Command Write cycle is loaded into the Address register
and the instruction then completes at that address. The
Address register will then increment, decrement, or stay at
the same value depending on the setting of Control Register
bits CT3 and CT2. If the Address Field flag is not set, the
memory access occurs at the address currently contained
in the Address register.
Control Register (CT)
The Control register is composed of a number of switches
that configure the LANCAM 1^ST, as shown in Table 7 on
page 15. It is written or read using a TCO CT instruction. If
bit 15 of the value written during a TCO CT is a 0, the
device is reset (and all other bits are ignored). See Table 4
for the Reset states. Bit 15 always reads back as a 0. A write
to the Control register causes an automatic compare to
occur (except in the case of a reset). Either the Foreground
or Background Control register will be active, depending
on which register set has been selected, and only the active
Control register will be written to or read from.
Control Register bits 8–6 control the CAM/RAM
partitioning. The CAM portion of each word may be sized
from a full 64 bits down to 16 bits in 16-bit increments. The
RAM portion can be at either end of the 64-bit word.
Compare masks may be selected by bits 5 and 4. Mask
Register 1, Mask Register 2, or neither may be selected to
mask compare operations. The address register behavior is
controlled by bits 3 and 2, and may be set to increment,
decrement, or neither after a memory access.
Segment Control Register (SC)
The Segment Control register, as shown in Table 8 on page
16, is accessed using a TCO SC instruction. On read cycles,
D15, D10, D5, and D2 will always read back as 0s. Either the
Foreground or Background Segment Control register will
be active, depending on which register set has been
selected, and only the active Segment Control register will
be written to or read from.
The Segment Control register contains dual independent
incrementing counters with limits, one for data reads and
one for data writes. These counters control which 16-bit
segment of the 64-bit internal resource is accessed during
a particular data cycle on the 16-bit data bus. The actual
destination for data writes and source for data reads (called
the persistent destination and source) are set independently
with SPD and SPS instructions, respectively.
Each of the two counters consists of a start limit, an end
limit, and the current count value that points to the segment
to be accessed on the next data cycle. The current count
value can be set to any segment, even if it is outside the
range set by the start and end limits. The counters count
up from the current count value to the end limit and then
jump back to the start limit. If the current count is greater
than the end limit, the current count value will increment to 3,
then roll over to 0 and continue incrementing until the end
limit is reached; it then jumps back to the start limit.
If a sequence of data writes or reads is interrupted, the Segment
Control register can be reset to its initial start limit values by
using an RSC instruction. After the LANCAM 1^ST is reset,
both Source and Destination counters are set to count from
Segment 0 to Segment 3 with an initial value of 0.
Address Register (AR)
The Address register points to the CAM memory location
to be operated upon when M@[AR] or M@aaaH is part of
the instruction. It can be loaded directly by using a TCO
AR instruction or indirectly by using an instruction requiring
an absolute address, such as MOV aaaH, CR,V. After being
loaded, the Address register value will then be used for the
next memory access referencing the Address register. A
reset sets the Address register to zero.
Rev. 1a
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