MT90820AL1 Zarlink Semiconductor, Inc., MT90820AL1 Datasheet - Page 9

• Manufacturer Part Number: MT90820AL1
• Description: Large Digital Switch
• Manufacturer: Zarlink Semiconductor, Inc.

MT90820
Data Sheet
Input Frame Offset Selection
Input frame offset selection allows the channel alignment of individual input streams to be offset with respect to the
output stream channel alignment (i.e., F0i). This feature is useful in compensating for variable path delays caused
by serial backplanes of variable lengths, which may be implemented in large centralized and distributed switching
systems.
Each input stream can have its own delay offset value by programming the frame input offset (FOR) registers.
Possible adjustment can range up to +4 master clock (CLK) periods forward with resolution of 1/2 clock period. The
output frame offset cannot be offset or adjusted. See Figure 4, Table 11 and Table 12 for delay offset programming.
Serial Input Frame Alignment Evaluation
The MT90820 provides the frame evaluation (FE) input to determine different data input delays with respect to the
frame pulse F0i.
A measurement cycle is started by setting the start frame evaluation (SFE) bit low for at least one frame. Then the
evaluation starts when the SFE bit in the IMS register is changed from low to high. Two frames later, the complete
frame evaluation (CFE) bit of the frame alignment register (FAR) changes from low to high to signal that a valid
offset measurement is ready to be read from bits 0 to 11 of the FAR register. The SFE bit must be set to zero before
a new measurement cycle started.
In ST-BUS mode, the falling edge of the frame measurement signal (FE) is evaluated against the falling edge of the
ST-BUS frame pulse. In GCI mode, the rising edge of FE is evaluated against the rising edge of the GCI frame
pulse. See Table 10 & Figure 3 for the description of the frame alignment register.
This feature is not available when the WFP Frame Alignment mode is enabled (i.e., when the WFPS pin is
connected to VDD).
Memory Block Programming
The MT90820 provides users with the capability of initializing the entire connection memory block in two frames.
Bits 11 to 15 of every connection memory location will be programmed with the pattern stored in bits 5 to 9 of the
IMS register.
The block programming mode is enabled by setting the memory block program (MBP) bit of the control register
high. When the block programming enable (BPE) bit of the IMS register is set to high, the block programming data
will be loaded into the bits 11 to 15 of every connection memory location. The other connection memory bits (bit 0 to
bit 10) are loaded with zeros. When the memory block programming is complete, the device resets the BPE bit to
zero.
Loopback Control
The loopback control (LPBK) bit of each connection memory location allows the ST-BUS output data to be looped
backed internally to the ST-BUS input for diagnostic purposes.
If the LPBK bit is high, the associated ST-BUS output channel data is internally looped back to the ST-BUS input
channel (i.e., data from STo n channel m will appear in STi n channel m). Note: when LPBK is activated in channel
m STo n+1 (for n even) or STo n-1 (for n odd), the data from channel m of STi n will be switched to channel m STo
n. The associated frame delay offset register must be set to zero for proper operation of the per-channel loopback
function. If the LPBK bit is low, the per-channel loopback feature is disabled and the device will function normally.
Delay Through the MT90820
The switching of information from the input serial streams to the output serial streams results in a throughput delay.
The device can be programmed to perform time-slot interchange functions with different throughput delay
capabilities on the per-channel basis. For voice application, select variable throughput delay to ensure minimum
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Zarlink Semiconductor Inc.