XRT72L50
SINGLE CHANNEL DS3/E3 FRAMER IC WITH HDLC CONTROLLER
á
PRELIMINARY
REV. P1.1.3
45
circuitry (within the user's system) should
assert the CS input pin of the Framer, by tog-
gling it "Low". This step enables further com-
munication between the μC/μP and the Framer
Microprocessor Interface block.
A.3
Assert the ALE_AS (Address Latch Enable) pin
by toggling it "High". This step enables the
Address Bus input drivers, within the Micropro-
cessor Interface block of the Framer.
A.4
After allowing the data on the Address Bus pins
to settle (by waiting the appropriate Address
Data Setup time), the μC/μP should then toggle
the ALE_AS pin "Low". This step latches the
contents, on the Address Bus pins, A[10:0], into
the XRT72L50 DS3/E3 Framer Microprocessor
Interface block. At this point, the initial address
of the burst access has now been selected.
N
OTE
:
The ALE_AS input pin should remain "Low" for the
remainder of this Burst Access operation.
A.5
Next, the μC/μP should indicate that this cur-
rent bus cycle is a Read Operation by toggling
the RD_DS (Read Strobe) input pin "Low".
This action also enables the bi-directional data
bus output drivers of the Framer device. At this
point, the bi-directional data bus output drivers
will proceed to drive the contents of the
addressed register onto the bi-directional data
bus, D[7:0].
A.6
Immediately after the μC/μP toggles the Read
Strobe signal "Low", the Framer device will tog-
gle the RDY_DTCK (READY) output pin "Low".
The Framer device does this in order to inform
the μC/μP that the data (to be read from the
data bus) is NOT READY to be latched into the
μC/μP
A.7
After some settling time, the data on the bi-
directional data bus will stabilize and can be
read by the μC/μP The XRT72L50 DS3/E3
Framer will indicate that this data is ready to be
read, by toggling the RDY_DTCK (Ready) sig-
nal "High".
A.8
After the μC/μP detects the RDY_DTCK signal
(from the XRT72L50 DS3/E3 Framer IC), it can
then will terminate the Read cycle by toggling
the RD_DS (Read Strobe) input pin "High".
Figure 29 presents an illustration of the behavior of
the Microprocessor Interface Signals, during the initial
Read Operation, within a Burst I/O Cycle for an Intel-
type μC/μP
At the completion of this initial read cycle, the μC/μP
has read in the contents of the first register or buffer
location (within the XRT72L50 DS3/E3 Framer) for
this particular burst I/O access operation. In order to
illustrate how this burst access operation works, the
byte (or word) of data, that is being read in Figure 29,
has been labeled Valid Data at Offset = 0x00. This
label indicates that the μC/μP is reading the very first
register (or buffer location) in this burst access opera-
tion.
2.2.2.2.1.1.2
The Subsequent Read Operations
The procedure that the μC/μP must use to perform
the remaining read cycles, within this Burst Access
operation, is presented below.
F
IGURE
29. B
EHAVIOR
OF
THE
M
ICROPROCESSOR
I
NTERFACE
S
IGNALS
,
DURING
THE
I
NITIAL
R
EAD
O
PERATION
OF
A
B
URST
C
YCLE
(I
NTEL
T
YPE
P
ROCESSOR
)
RDY_DTCK
ALE_AS
A(8:0)
CS
D(7:0)
RD_DS
WR_R/W
Not Valid
Address of "Initial" Target Register (Offset = 0x00)
Valid Data of
Offset = 0x00