WidePort LANCAM® Family
OPERATIONAL CHARACTERISTICS Continued
in Enhanced mode, it is not necessary to unlock the daisy
chain with a NOP instruction before command or data writes
after a non-matching compare, as required in Standard mode.
Device Select Register (DS)
The Device Select register is used to select a specific (target)
device using the TCO DS instruction in DQ31–16 and
setting the 16-bit DS value in DQ15–0 equal to the target’s
PA value. The DS register can be read through DQ15–0
with DQ31–16 returning the upper 16 bits of the Status
register. In a daisy chain, setting DS = FFFFH will select all
devices. However, in this case, the ability to read information
out of the device is restricted as shown in Tables 6a and 6b.
A software reset (using the Control register) does not affect
the Device Select register.
Segment Control Register (SC)
The Segment Control register, as shown in Table 10, is
accessed using a TCO SC instruction with the register contents
placed on DQ15–0. On read cycles, DQ31–16 will be the upper
16 bits of the Status register, and D15, D10, D5, and D2 always
read back as 0s. Reserved locations D14, D12, D9, D7, D4, and
D1 should always be set to 0 and as such will also 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.
Address Register (AR)
The Address register points to the CAM memory location
to be operated upon when a 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. The AR
register can be read through DQ15–0 with DQ31–16
returning the upper 16 bits of the Status register. 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.
The Segment Control register contains dual independent
incrementing counters with limits, one for data reads and
one for data writes. These counters control which 32-bit
segment of the 64-bit internal resource is accessed during
a particular data cycle on the 32-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.
Control Register bits CT3 and CT2 set the address to
automatically increment or decrement (or not change)
during sequences of Command or Data cycles. The Address
register will change after executing an introduction that
includes M@[AR] or M@aaaH, or after a data access to
the end limit segment (as set in the Segment Control
register) when the persistent source or destination is
M@[AR] or M@aaaH.
Each of the two counters consists of a start limit, an end
limit, and the current segment pointer, each a single bit
representing either the lower segment (0) or the upper
segment (1). The current segment pointer can be set to
either 0 or 1 even if that value is outside the range set by
the start and end segments. The counters count up from
the current segment pointer to the end limit and then roll
over back to the start limit.
Either the Foreground or Background Address register will
be active, depending on which register set has been
selected, and only the active Address register will be written
to or read from.
If a sequence of data writes or reads is interrupted, the
Segment Control register can be reset to its initial start limit
values with the RSC instruction. After a reset, both Source
and Destination counters are set to count from Segment 0
to Segment 1 with an initial value of 0.
Next Free Address Register (NF)
The WidePort LANCAM automatically stores the address
of the first empty memory location in the Next Free Address
register, which is then used as a memory address pointer
for M@NF operations. The Next Free Address register,
shown in Table 11, can be read through DQ15–0 using a TCO
NF instruction. DQ31–16 will return the upper 16 bits of the
Status register. By taking /EC LOW during the TCO NF
instruction cycle, only the device with /FI LOW and /FF
HIGH will output the contents of its Next Free Address
register, which gives the Next Free address in a system of
daisy-chained devices. The Next Free address may be read
from a specific device in the chain by setting the Device
Page Address Register (PA)
The Page Address register is loaded using a TCO PA
instruction on DQ31–16 with a user selected 16-bit value
(not FFFFH) on DQ15–0. During reads of the PA register,
DQ31–16 will all be 0. The entry in the PA register is used to
give a unique address to the different devices in a daisy
chain. In a daisy chain, the PA value of each device is
loaded using the SFF instruction to advance to the next
device, as shown in the “Setting Page Address Register
Values” section. A software reset (using the Control
register) does not affect the Page Address register.
Rev. 2
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