MITEL MT8809AC, MT8809AE, MT8809AP Datasheet



CMOS ST-BUS FAMILY

MT8985

Enhanced Digital Switch

Features

• 256 x 256 channel non-blocking switch

• Programmable frame integrity for wideband channels

• Automatic identiﬁcation of ST-BUS/GCI interface backplanes

• Per channel tristate control

• Patented message mode

• Non-multiplexed microprocessor interface

• Single +5 volt supply

• Available in DIP-40, PLCC-44 and QFP-44 packages

• Pin compatible with MT8980 device

Applications

• Medium size digital switch matrices

• Hyperchannel switching (e.g., ISDN H0)

• ST-BUS/MVIP™ interface functions

• Serial bus control and monitoring

• Centralized voice processing systems

• Data multiplexer

ISSUE 5 March 1997

Ordering Information

MT8985AE 40 Pin Plastic DIP MT8985AP 44 Pin PLCC MT8985AL 44 Pin QFP

-40°C to +85°C

Description

The MT8985 Enhanced Digital Switch device is an upgraded version of the popular MT8980D Digital Switch (DX). It is pin compatible with the MT8980D and retains all of the MT8980D's functionality. This VLSI device is designed for switching PCM-encoded voice or data, under microprocessor control, in digital exchanges, PBXs and any ST-BUS/MVIP environment. It provides simultaneous connections for up to 256 64kb/s channels. Each of the eight serial inputs and outputs consist of 32 64 kbit/s channels multiplexed to form a 2048 kbit/s stream. As the main function in switching applications, the device provides per-channel selection between variable or constant throughput delays. The constant throughput delay feature allows grouped channels such as ISDN H0 to be switched through the device maintaining its sequence integrity. The MT8985 is ideal for medium sized mixed voice/data switch and voice processing applications.

STi0 STi1 STi2 STi3 STi4 STi5 STi6 STi7

Serial

Parallel

Converter

Data

Memory

F0i

C4i

Frame

Counter

Control Register

Control Interface

CS R/W A5/A0DTA D7/

Figure 1 - Functional Block Diagram

Output

MUX

Connection

Memory

CSTo

ODE

Parallel

Serial

Converter

STo0 STo1 STo2 STo3 STo4 STo5 STo6 STo7

2-45

MT8985

STi2

STi1

STi0

DTA

ODE

CSTo

STo1

STo0

STo2

STi2

STi1

STi0

DTA

ODE

CSTo

STo1

STo0

STo2

STi3 STi4 STi5 STi6 STi7 VDD

F0i

C4i

A0 A1 A2

7 8 9 10 11 12 13 14 15 16 17

16 5 4 3 2 4443424140

231819 20 2122 24 25 26 2728

44 PIN PLCC

39 38 37 36 35 34 33 32 31 30 29

STo3 STo4 STo5 STo6 STo7 VSS D0 D1 D2 D3 D4

DTA STi0 STi1 STi2 STi3 STi4 STi5 STi6 STi7

VDD

C4i

1 2 3 4

5 6

7 8

9 10 11

F0i

12 13

40 PIN PLASTIC DIP

40 39

38 37 36 35 34 33 32 31 30 29 28 27 26 25 24 23 22 21

STi3

STi4 STi5 STi6 STi7 VDD

F0i

C4i

A0 A1 A2

CSTo ODE STo0 STo1 STo2 STo3 STo4 STo5 STo6 STo7 VSS D0 D1 D2 D3 D4 D5 D6 D7

4443424140

2 3 4 5 6 7 8 9 10 11

1213141516

44 PIN QFP

3837363534

1819202122

33 32 31 30 29 28 27 26 25 24 23

STo3 STo4 STo5 STo6 STo7 VSS D0 D1 D2 D3 D4

Figure 2 - Pin Connections

Pin Description

Pin #

DIP44PLCC44QFP

1240DTA Data Acknowledgement (Open Drain Output). This active low output indicates that

2-9 3-5

41-43

7-11

10 12 6 V 11 13 7 F0i Frame Pulse (Input): This input accepts and automatically identiﬁes frame

12 14 8 C4i Clock (Input). 4.096 MHz serial clock for shifting data in and out of the data streams.

13-18 15-17

19-21

13-15

19 22 16 DS Data Strobe (Input). This is the input for the active high data strobe on the

20 23 17 R/W Read/Write (Input). This input controls the direction of the data bus lines (D0-D7)

Name Description

a data bus transfer is complete. A pull-up resistor is required at this output.

1-5

STi0-

STi7

ST-BUS Input 0 to 7 (Inputs). Serial data input streams. These streams have 32 channels at data rates of 2.048 Mbit/s.

+5 Volt Power Supply rail.

synchronization signals formatted according to different backplane speciﬁcations such as ST-BUS and GCI.

9-11

A0-A5 Address 0 to 5 (Inputs). These lines provide the address to MT8985 internal

registers.

microprocessor interface. This input operates withCS to enable the internal read and write generation.

during a microprocessor access.

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MT8985

Pin Description

Pin #

40

DIP44PLCC44QFP

21 24 18 CS Chip Select (Input). Active low input enabling a microprocessor read or write of

22-29 25-27

29-33

30 34 28 V

31-38 35-39

41-43

39 44 38 ODE Output Drive Enable (Input). This is an output enable for the STo0 to STo7 serial

40 1 39 CSTo Control ST-BUS Output (Output). This output is a 2.048 Mb/s line which contains

6, 18,

19-21 23-27

29-33 35-37

12,22

28,

Name Description

control register or internal memories.

D7-D0 Data Bus 7 to 0 (Bidirectional). These pins provide microprocessor access to data

in the internal control register, connect memory high, connect memory low and data memory.

Ground Rail.

STo7-

STo0

34,

ST-BUS Outputs 7 to 0 (Three-state Outputs). Serial data output streams. These streams are composed of 32 channels at data rates of 2.048 Mbit/s.

outputs. If this input is low STo0-7 are high impedance. If this input is high each channel may still be put into high impedance by software control.

256 bits per frame. The level of each bit is controlled by the contents of the CSTo bit in the Connect Memory high locations.

NC No Connection.

Functional Description

With the integration of voice, video and data services into the same network, there has been an increasing demand for systems which ensure that data at N x 64 Kbit/s rates maintain frame sequence integrity while being transported through time slot interchange circuits. Existing requirements demand time slot interchange devices performing switching with constant throughput delay while guaranteeing minimum delay for voice channels.

The MT8985 device provides both functions and allows existing systems based on the MT8980D to be easily upgraded to maintain the data integrity while multiple channel data are transported. The device is designed to switch 64 kbit/s PCM or N x 64 kbit/s data. The MT8985 can provide both frame integrity for data applications and minimum throughput switching delay for voice applications on a per channel basis.

By using Mitel Message mode capability, the microprocessor can access input and output time slots on a per channel basis to control devices such as the MITEL MT8972, ISDN Transceivers and T1/ CEPT trunk interfaces through the ST-BUS interface. Different digital backplanes can be accepted by the MT8985 device without user's intervention. The MT8985 device provides an internal circuit that

automatically identiﬁes the polarity and format of frame synchronization input signals compatible to ST-BUS and GCI interfaces.

Device Operation

A functional block diagram of the MT8985 device is shown in Figure 1. The serial ST-BUS streams operate continuously at 2.048 Mb/s and are arranged in 125 µs wide frames each containing 32 8-bit channels. Eight input (STi0-7) and eight output (STo0-7) serial streams are provided in the MT8985 device allowing a complete 256 x 256 channel nonblocking switch matrix to be constructed. The serial interface clock for the device is 4.096 MHz, as required in ST-BUS and GCI speciﬁcations.

Data Memory

The received serial data is converted to parallel format by the on-chip serial to parallel converters and stored sequentially in a 256-position Data Memory. The sequential addressing of the Data Memory is generated by an internal counter that is reset by the input 8 kHz frame pulse (F0i) marking the frame boundaries of the incoming serial data streams.

Depending on the type of information to be switched, the MT8985 device can be programmed to perform

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MT8985

time slot interchange functions with different throughput delay capabilities on a per-channel basis. For voice applications, the variable delay mode can be selected ensuring minimum throughput delay between input and output data. In multiple or grouped channel data applications, the constant delay mode can be selected maintaining the integrity of the information through the switch.

Data to be output on the serial streams may come from two sources: Data Memory or Connect Memory. Locations in the Connect Memory, which is split into HIGH and LOW parts, are associated with particular ST-BUS output streams. When a channel is due to be transmitted on an ST-BUS output, the data for the channel can either be switched from an ST-BUS input (connection mode) or it can be originated from the microprocessor (message mode). If a channel is conﬁgured in connection mode, the source of the output data is the Data Memory. If a channel is conﬁgured in message mode, the source of the output data is the Connect Memory Low. Data destined for a particular channel on the serial output stream is read from the Data or Connect Memory Low during the previous channel time slot. This allows enough time for memory access and internal parallel to serial conversion.

three-state condition. In addition, the Connect Memory High provides one bit to allow the user to control the state of the CSTo output pin.

If an output channel is set to three-state condition, the TDM serial stream output will be placed in high impedance during that channel time. In addition to the per-channel three-state control, all channels on the TDM outputs can be placed in high impedance at one time by pulling the ODE input pin in LOW. This overrides the individual per-channel programming on the Connect Memory High bits.

The Connect Memory data is received via the Microprocessor Interface at D0-D7 lines. The addressing of the MT8985 internal registers, Data and Connect memories is performed through address input pins and some bits of the device's Control register. The higher order address bits come from the Control register, which may be written or read through the microprocessor interface. The low er order address bits come directly from the external address line inputs. For details on the device addressing, see Software Control and Control register description.

Serial Interface Timing

Connection and Message Modes

In connection mode, the addresses of input source for all output channels are stored in the Connect memory Low. The Connect Memory Low locations are mapped to each location corresponding to an output 64 kb/s channel. The contents of the Data memory at the selected address are then transferred to the parallel to serial converters. By having the output channel to specify the input channel through the connect memory, the user can route the same input channel to several output channels, allowing broadcasting facility in the switch.

In message mode the CPU writes data to the Connect Memory Low locations which correspond to the output link and channel number. The contents of the Connect Memory Low are transferred to the parallel to serial converter one channel before it is to be output. The Connect Memory Low data is transmitted each frame to the output until it is changed by the CPU.

The per-channel functions available in the MT8985 are controlled by the Connect Memory High bits, which determine whether individual output channels are selected into speciﬁc conditions such as: message or connection mode, variable or constant throughput delay modes, output drivers enabled or in

The MT8985 master clock (C4i) is a 4.096 MHz allowing serial data link conﬁguration at 2.048 Mb/s to be implemented. The MT8985 frame synchronization pulse can be formatted according to ST-BUS or GCI interface speciﬁcations; i.e., the frame pulse can be active in HIGH (GCI) or LOW (ST-BUS). The MT8985 device automatically detects the presence of an input frame pulse and identiﬁes the type of backplane present on the serial interface. Upon determining the correct interface connected to the serial port, the internal timing unit establishes the appropriate serial data bit transmit and sampling edges. In ST-BUS mode, every second falling edge of the 4.096 MHz clock marks a bit boundary and the input data is clocked in by the rising edge, three quarters of the way into the bit cell. In GCI mode, every second rising edge of the 4.096 MHz clock marks the bit boundary while data sampling is performed during the falling edge, at three quarters of the bit boundaries.

Delay through the MT8985

The transfer of information from the input serial streams to the output serial streams results in a delay through the MT8985 device. The delay through the MT8985 device varies according to the mode selected in the V/C bit of the connect memory high.

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MT8985

Variable Delay mode

The delay in this mode is dependent only on the combination of source and destination channels and it is not dependent on the input and output streams. The minimum delay achie vable in the MT8985 de vice is 3 time slots. In the MT8985 device, the information that is to be output in the same channel position as the information is input (position n), relative to frame pulse, will be output in the following frame (channel n, frame n+1). The same occurs if the input channel has to be output in the two channels succeeding (n+1 and n+2) the channel position as the information is input.

The information switched to the third timeslot after the input has entered the device (for instance, input channel 0 to output channel 3 or input channel 30 to output channel 1), is always output three channels later.

Any switching conﬁguration that provides three or more timeslots between input and output channels, will have a throughput delay equal to the difference between the output and input channels; i.e., the throughput delay will be less than one frame. Table 1 shows the possible delays for the MT8985 device in Variable Delay mode:

Input

Channel

n m=n, n+1 or

n m>n+2 m-n time slots n m<n 32-(n-m) time slots

Output

Channel

n+2

Table 1

Throughput Delay

m-n + 32 timeslots

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 Mitel 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.

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 achiev-able 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 s witched to the destination time slot on

A5 A4 A3 A2 A1 A0 LOCATION

Control Register

•

Figure 3 - Address Memory Map

Note: "x" Don’t care

Software Control

The address lines on the microprocessor interface give access to the MT8985 internal registers and memories. If the A5,A1,A0 address line inputs are

Channel 0 Channel 1

•

Channel 31

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MT8985

LOW, then the MT8985 Inter nal Control Register is addressed (see Figure 3). If A5 input line is HIGH, then the remaining address input lines are used to select Memory subsections of 32 locations corresponding to the number of channels per input or output stream. As explained in the Control register description, the address input lines and the Stream Address bits (STA) of the Control register give the user the capability of selecting all positions of the MT8985 Data and Connect memories.

The data in the Control register consists of Split memory and Message mode bits, Memory select and Stream Address bits (see Figure 4). The memory select bits allow the Connect Memory HIGH or LOW or the Data Memory to be chosen, and the Stream Address bits deﬁne an internal memory subsections corresponding to input or output ST-BUS streams. Bit 7 (Split Memory) of the Control register allows split memory operation whereby reads are from the Data memory and writes are to the Connect Memor y LOW.

The Message Enable bit (bit 6) places every output channel on every output stream in message mode; i.e., the contents of the Connect Memory LOW

(CML) are output on the ST-BUS output streams once every frame unless the ODE input pin is LOW. If ME bit is HIGH, then the MT8985 behaves as if bits 2 (Message Channel) and 0 (Output Enable) of every Connect Memory HIGH (CMH) locations were set to HIGH, regardless of the actual value. If ME bit is LOW, then bit 2 and 0 of each Connect Memory HIGH location operates normally. In this case, if bit 2 of the CMH is HIGH, the associated ST-BUS output channel is in Message mode. If bit 2 of the CMH is LOW, then the contents of the CML deﬁne the source information (stream and channel) of the time slot that is to be switched to an output.

If the ODE input pin is LOW, then all ser ial outputs are high-impedance. If ODE is HIGH, then bit 0 (Output Enable) of the CMH location enables (if HIGH) or disables (if LOW) the output drivers for the corresponding individual ST-BUS output stream and channel.

The contents of bit 1 (CSTo) of each Connection Memory High location (see Figure 5) is output on CSTo pin once every frame. The CSTo pin is a 2048 Mbit/s output which carries 256 bits. If CSTo bit is set HIGH, the corresponding bit on CSTo output is

76543210

SM ME X MS1 MS0 STA2 STA1 STA0

BIT NAME DESCRIPTION

7 SM Split Memory . When 1, all subsequent reads are from the Data Memory and writes are to

the Connection Memory Low, except when the Control Register is accessed again. The Memory Select bits need to be set to specify the memory for the operations. When 0, the Memory Select bits specify the memory for subsequent operations. In either case, the Stream Address Bits select the subsection of the memory which is made available.

6 ME Message Enable. When 1, the contents of the Connection Memory Low are output on the

Serial Output streams except when in High Impedance. When 0, the Connection Memory bits for each channel determine what is output.

4-3 MS1-MS0 Memory Select Bits. The memory select bits operate as follows:

0-0 - Not to be used

0-1 - Data Memory (read only from the CPU) 1-0 - Connection Memory Low 1-1 - Connection Memory High

2-0 STA2-0 Stream Address Bits 2-0. The number expressed in binary notation on these bits refers to

the input or output ST-BUS stream which corresponds to the subsection of memory made accessible for subsequent operations.

x = Don’t care

Figure 4 - Control Register Bits

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