DS2175
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PIN Description Table 1
PIN SYMBOL TYPE DESCRIPTION
1 RCLKSEL I Receive Clock Select. Tie to V
SS
for 1.544 MHz applications, to
V
DD
for 2.048 MHz.
2 RCLK I Receive Clock. 1.544 or 2.048 MHz data clock.
3 RSER I Receive Serial Data. Sampled on falling edge of RCLK.
4 RMSYNC I Receive Multifram Sync. Rising edge establishes receive side
frame and multiframe boundaries.
5 FSD O Frame Slip Directions. State indicates direction of last slip;
latched on slip occurrence.
6
SLIP
O Frame Slip. Active low, open collector output. Held low for 65
SYSCLK cycles when a slip occurs.
7
ALN
I Align. Recenters buffer on next system side frame boundary when
forced low; negative edge-triggered.
8 V
SS
– Signal Ground. 0.0 volts.
9 SCLKSEL I System Clock Select. Tie to V
SS
for 1.544 MHz applications, to
V
DD
for 2.048 MHz.
10
S/
I Serial/Parallel Select. Tie to V
SS
for parallel backplane
applications, to V
DD
for serial.
11 SCHCLK O System Channel Clock. Transitions high on channel boundaries;
useful for serial to parallel conversion of channel data.
12 SFSYNC I System Frame Sync. Rising edge establishes system side frame
boundaries.
13 SMSYNC O System Multiframe Sync. Slip-compensated multiframe output;
used with RMSYNC to monitor depth of store real time.
14 SSER O System Serial Data. Updated on rising edge of SYSCLK.
15 SYSCLK I System Clock. 1.544 or 2.048 MHz data clock.
16 V
DD
– Positive Supply. 5.0 volts.
PCM BUFFER
The DS2175 utilizes a 2–frame buffer to synchronize in-coming PCM data to the system backplane clock.
Buffer depth is mode–dependent; 2.048 MHz to 2.048 MHz applications utilize 64 bytes of buffer
memory, while all other modes are supported by 48 bytes. The buffer samples data at RSER on the falling
edge of RCLK. Output data appears at SSER and is updated on the rising edge of SYSCLK. The buffer
depth is constantly monitored by onboard contention logic; a “slip” occurs when the buffer is completely
emptied or filled. Slips automatically recenter the buffer to a one–frame depth and always occur on frame
boundaries.
DATA FORMAT
Data is presented to, and output from, the elastic store in a “framed” format. A rising edge at RMSYNC
and SFSYNC establishes frame boundaries for the receive and system sides. North American (T1) frames
contain 24 data channels of 8 bits each and an F–bit (193 bits total). European (CEPT) frames contain 32
data channels (256 bits). The frame rate of both systems is 8 KHz. RMSYNC and SFSYNC do not
require a pulse at every frame boundary; if desired, they may be pulsed once to establish frame alignment.
Internal counters will then maintain the frame alignment and may be reinforced by the next rising edge at
RMSYNC and/or SFSYNC.
