MT8985

Data Sheet

6

Zarlink Semiconductor Inc.

Table 1 - Channel Delay for the Variable Mode Delay

Constant Delay Mode

In this mode frame integrity is maintained in all switching configurations by making use of a multiple Data-Memory

buffer technique where input channels written in any of the buffers during frame N will be read out during frame

N+2. In the MT8985, the minimum throughput delay achievable in Constant Delay mode will be 32 time slots; for

example, when input time slot 32 (channel 31) is switched to output time slot 1 (channel 0). Likewise, the maximum

delay is achieved when the first time slot in a frame (channel 0) is switched to the last time slot in the frame

(channel 31), resulting in 94 time slots of delay.

To summarize, any input time slot from input frame N will be always switched to the destination time slot on output

frame N+2. In Constant Delay mode, the device throughput delay is calculated according to the following formula:

DELAY = [32 + (32 - IN) + (OUT - 1)];

(expressed in number of time slots)

Where:

IN is the number of the input time slot

(from 1 to 32).

OUT is the number of the output time slot

(from 1 to 32).

Microprocessor Port

The MT8985 microprocessor port has pin compatibility with Zarlink MT8980 Digital Switch device providing a non-

multiplexed bus architecture. The parallel port consists of an 8 bit parallel data bus (D0-D7), six address input lines

(A0-A5) and four control lines (CS, DS, R/W and DTA). This parallel microport allows the access to the Control

registers, Connection Memory High, Connection Memory Low and the Data Memory. All locations are read/written

except for the data memory which can be read only.

Accesses from the microport to the connection memory and the data memory are multiplexed with accesses from

the input and output TDM ports. This can cause variable Data Acknowledge delays (DTA). In the MT8985 device,

the DTA output provides a maximum acknowledgement delay of 800 ns for read/write operations in the Connection

Memory. However, for operations in the Data Memory (Message Mode), the maximum acknowledgement delay can

be 1220 ns.

Input

Channel

Output Channel

Throughput Delay

n

m=n, n+1 or n+2

m-n + 32 timeslots

nm>n+2

m-n time slots

n

m<n

32-(n-m) time slots