LANCAM A/L series (not recommended for new designs)
Operational Characteristics
OPERATIONAL CHARACTERISTICS
Note: Throughout the following, “aaaH” represents a three-digit hexadecimal number “aaa,” while “bbB” represents a two-digit
binary number “bb.” All memory locations are written to or read from in 16-bit segments. Segment 0 corresponds to the lowest order
bits (bits 15–0) and Segment 3 corresponds to the highest order bits (bits 63–48).
Control Bus
The Register Set
Refer to Figure 1 on page 1 for the following discussion.
The inputs Chip Enable (/E), Write Enable (/W),
Command Enable (/CM), and Enable Daisy Chain (/EC)
are the primary control mechanism for the LANCAM. The
/EC input of the Control bus enables the /MF Match flag
output when LOW and controls the daisy chain operation.
Instructions are the secondary control mechanism. Logical
combinations of the Control Bus inputs, coupled with the
execution of Select Persistent Source (SPS), Select
Persistent Destination (SPD), and Temporary Command
Override (TCO) instructions allow the I/O operations to
and from the DQ15–0 lines to the internal resources, as
shown in Table 2.
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
causes 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.
The Comparand register is the default source and
destination for Data Read and Write cycles. This default
state can be overridden independently by executing a
Select Persistent Source or Select Persistent Destination
instruction, selecting a different source or destination for
data. Subsequent Data Read or Data Write cycles access
that source or destination until another SPS or SPD
instruction is executed. The currently selected persistent
source or destination can be read back through a TCO PS
or PD instruction. The sources and destinations available
for persistent access are those resources on the 64-bit bus:
Comparand register, Mask Register 1, Mask Register 2,
and the Memory array.
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 then increments, decrements, or stays
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.
The default destination for Command Write cycles is the
Instruction decoder, while the default source for
Command Read cycles is the Status register.
Temporary Command Override (TCO) instructions
provide access to the Control register, the Page Address
register, the Segment Control register, the Address
register, the Next Free Address register, and Device Select
register. TCO instructions are active only for one
Command Read or Write cycle after being loaded into the
Instruction decoder.
Control Register (CT)
The Control register contains a number of switches that
configure the LANCAM, as shown in Control Register
Bits on page 23. 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 3 on page 11 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 is
active, depending on which register set has been selected,
and only the active Control register is written to or read
from.
The data and control interfaces to the LANCAM are
synchronous. During a Write cycle, the Control and Data
inputs are registered by the falling edge of /E. When
writing to the persistently selected data destination, the
Destination Segment counter is clocked by the rising edge
of /E. During a Read cycle, the Control inputs are
registered by the falling edge of /E, and the Data outputs
are enabled while /E is LOW. When reading from the
persistently selected data source, the Source Segment
counter is clocked by the rising edge of /E.
If the Match Flag is disabled through bit 14 and bit 13, the
internal match condition, /MA(int), used to determine a
daisy-chained device’s response is forced HIGH as shown
in Table 4 so that Case 6 is not possible, effectively
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Rev. 1
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