WidePort LANCAM® Family
OPERATIONAL CHARACTERISTICS Continued
Setting Page Address Register Values
Vertically Cascaded System Initialization
Table 7 shows an example of code that initializes a daisy-
chained string of WidePort LANCAM devices. The
initialization example shows how to set the Page Address
registers of each of the devices in the chain through the
use of the Set Full Flag instruction, and how the Control
registers and Segment counters of all the WidePort
LANCAM devices are set for a typical application. Each
Page Address register must contain a unique value (not
FFFFH) to prevent bus contention.
In a vertically cascaded system, the user must set the
individual Page Address registers to unique values by
using the Page Address initialization mechanism. Each Page
Address register must contain a unique value to prevent
bus contention. This process allows individual device
selection. The Page Address register initialization works
as follows: Writes to Page Address registers are only active
for devices with /FI LOW and /FF HIGH. At initialization,
all devices are empty, thus the top device in the string will
respond to a TCO PA instruction, and load its PA register.
To advance to the next device in the string, a Set Full Flag
(SFF) instruction is used, which is also only active for the
device with /FI LOW and /FF HIGH. The SFF instruction
changes the first device’s /FF to LOW, although the device
really is empty, which allows the next device in the string to
respond to the TCO PA instruction and load its PA register.
The initialization proceeds through the chain in a similar
manner filling all the PA registers in turn. Each device must
have a unique Page Address value stored in its PA register,
or contention will result. After all the PA registers are filled,
the entire string is reset through the Control register, which
does not change the values stored in the individual PA
registers. After the reset, the Device Select registers are
usually set to FFFFH to enable operation, in Case 1 of Table
6a. The Control registers and the Segment Control
registers are then set to their normal operating values
for the application.
For typical daisy chain operation, data is loaded into the
Comparand registers of all the devices in a string
simultaneously by setting DS=FFFFH. Since reading is
prohibited when DS=FFFFH except for the device with a
match, for a diagnostic operation you need to select a
specific device by setting DS=PA for the desired device
to be able to read from it. Refer to Tables 6a and 6b for
preconditions for reading and writing.
Initialization for a single WidePort LANCAM is similar.
The Device Select register in this case is usually set to
equal the Page Address register for normal operations.
Also, the dedicated /MA flag output can be used instead
of /MF, allowing /EC to be tied HIGH.
Cycle Type
Op-Code
Data Bus
Comments
Notes
DQ31–16 DQ15–0
Command Write
Command Write
Command Write
Command Write
TCO DS
TCO CT
TCO PA
SFF
Target Device Select register and disable local device selection
Target Control register and reset
0A28H
0A00H
0A08H
0700H
FFFFH
0000H
nnnnH
X
1
2
2
Target Page Address register and set page for cascaded operation
Set Full flag; allows access to next device (repeat previous cycle
plus this one for each device in chain)
•
•
Command Write
Command Write
Command Write
TCO CT
TCO CT
TCO SC
Target Control register and reset Full flags, but not Page address
Target Control register and give initial values
Target Segment counter and set destination to only use upper
segment and source to only use lower segment
0A00H
0A00H
0A10H
0000H
8080H
2808H
3
4
Command Write
Set Persistent source to Memory at the Highest-Priority match
SPS M@HM
0005H
X
Notes:
1. Toggling the /RESET pin generates the same effect as this reset of the Control register, but good programming practice dictates
a software reset for initialization to account for all possible prior conditions.
2. This instruction may be omitted for a single WidePort LANCAM application. The last SFF will cause the /FF pin in the last chip in
a daisy chain to go LOW. In a daisy chain, DS needs to be set equal to PA to read out a particular chip prior to a match condition.
3. Typical WidePort LANCAM control environment: Enable match flag; Enable full flag; 32 CAM bits/32 RAM bits; Disable comparison
masking; and Enable address increment. This example translates to 8080H. See Table 9 for Control Register bit
assignments.
4. Setting the persistent source to the Memory at Highest-Priority match allows a compare operation to be followed by a read of the
associated data when a match is found. Note that the persistent destination is set to the Comparand register by the reset.
Table 7: Example Initialization Routine
Rev. 2
16
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