MITEL MH80626C Datasheet



ISO-CMOS ST-BUS FAMILY

MT8980D

Digital Switch

Features

• Mitel ST-BUS compatible

• 8-line x 32-channel inputs

• 8-line x 32-channel outputs

• 256 ports non-blocking switch

• Single power supply (+5 V)

• Low power consumption: 30 mW Typ.

• Microprocessor-control interface

• Three-state serial outputs

ISSUE8 March 1997

Ordering Information

MT8980DE 40 Pin Plastic DIP MT8980DP 44 Pin PLCC

-40°C to +85°C

Description

This VLSI ISO-CMOS device is designed for switching PCM-encoded voice or data, under microprocessor control, in a modern digital exchange, PBX or Central Ofﬁce. It provides simultaneous connections for up to 256 64 kbit/s channels. Each of the eight serial inputs and outputs consist of 32 64 kbit/s channels multiplexed to form a 2048 kbit/s ST-BUS stream. In addition, the MT8980 provides microprocessor read and write access to individual ST-BUS channels.

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

2-3

MT8980D

STi3 STi4 STi5 STi6 STi7 VDD

F0i

C4i

A0 A1 A2

7 8 9 10 11 12 13 14 15 16 17

Pin Description

Pin #

DIP44PLCC

Name Description

STi1

STi2

65432

1819202122

DTA

STi0

44 PIN PLCC

ODE

CSTo

W R/

STo1

STo0

4443424140

2425262728

STo2

STo3

STo4

STo5

STo6

STo7

VSS

Figure 2 - Pin Connections

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

15

17

18

40 PIN PLASTIC DIP

40 39

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

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

12DTA Data Acknowledgement (Open Drain Output). This is the data acknowledgement on the

microprocessor interface. This pin is pulled low to signal that the chip has processed the data. A 909 Ω, 1/4W, resistor is recommended to be used as a pullup.

2-4 3-5 STi0-

STi2

5-9 7-11 STi3-

STi7

10 12 V

ST-BUS Input 0 to 2 (Inputs). These are the inputs for the 2048 kbit/s ST-BUS input streams.

ST-BUS Input 3 to 7 (Inputs). These are the inputs for the 2048 kbit/s ST-BUS input streams.

Power Input. Positive Supply.

11 13 F0i Framing 0-Type (Input). This is the input for the frame synchronization pulse for the

2048 kbit/s ST-BUS streams. A low on this input causes the internal counter to reset on the next negative transition of C4i.

12 14 C4i 4.096 MHz Clock (Input). ST-BUS bit cell boundaries lie on the alternate falling edges of this

clock.

13-1515-17A0-A2 Address 0 to 2 (Inputs). These are the inputs for the address lines on the microprocessor

interface.

16-1819-21A3-A5 Address 3 to 5 (Inputs). These are the inputs for the address lines on the microprocessor

interface.

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

interface.

20 23 R/W Read or Write (Input). This is the input for the read/write signal on the microprocessor

interface - high for read, low for write.

21 24 CS Chip Select (Input). This is the input for the active low chip select on the microprocessor

interface

2-4

Pin Description (continued)

Pin #

40

DIP44PLCC

22-2425-27D7-D5 Data 7 to 5 (Three-state I/O Pins). These are the bidirectional data pins on the

25-2929-33D4-D0 Data 4 to 0 (Three-state I/O Pins). These are the bidirectional data pins on the

Name Description

microprocessor interface.

MT8980D

30 34 V

31-3535-39STo7-

STo3

36-3841-43STo2-

STo0

39 44 ODE Output Drive Enable (Input).If this input is held high, the STo0-STo7 output drivers function

40 1 CSTo Control ST-BUS Output (Complementary Output). Each frame of 256 bits on this ST-BUS

6, 18,

28,

Power Input. Negative Supply (Ground).

ST-BUS Output 7 to 3 (Three-state Outputs). These are the pins for the eight 2048 kbit/s ST-BUS output streams.

ST-BUS Output 2 to 0 (Three-state Outputs). These are the pins for the eight 2048 kbit/s ST-BUS output streams.

normally . If this input is lo w, the ST o0-STo7 output drivers go into their high impedance state . NB: Even when ODE is high, channels on the STo0-STo7 outputs can go high impedance under software control.

output contains the values of bit 1 in the 256 locations of the Connection Memory High.

NC No Connection.

2-5

MT8980D

Functional Description

In recent years, there has been a trend in telephony towards digital switching, particularly in association with software control. Simultaneously, there has been a trend in system architectures towards distributed processing or multi-processor systems.

In accordance with these trends, MITEL has devised the ST-BUS (Serial Telecom Bus). This bus architecture can be used both in software-controlled digital voice and data switching, and for interprocessor communications. The uses in switching and in interprocessor communications are completely integrated to allow for a simple general purpose architecture appropriate for the systems of the future.

The serial streams of the ST-BUS operate continuously at 2048 kbit/s and are arranged in 125 µs wide frames which contain 32 8-bit channels. MITEL manufactures a number of devices which interface to the ST-BUS; a key device being the MT8980 chip.

The MT8980 can switch data from channels on STBUS inputs to channels on ST-BUS outputs, and simultaneously allows its controlling microprocessor to read channels on ST-BUS inputs or write to channels on ST-BUS outputs (Message Mode). To the microprocessor, the MT8980 looks lik e a memory peripheral. The microprocessor can write to the MT8980 to establish switched connections between input ST-BUS channels and output ST-BUS channels, or to transmit messages on output ST-BUS channels. By reading from the MT8980, the microprocessor can receive messages from ST-BUS input channels or check which switched connections have already been established.

By integrating both switching and interprocessor communications, the MT8980 allows systems to use distributed processing and to switch voice or data in an ST-BUS architecture.

Hardware Description

Serial data at 2048 kbit/s is received at the eight STBUS inputs (STi0 to STi7), and serial data is transmitted at the eight ST-BUS outputs (STo0 to STo7). Each serial input accepts 32 channels of digital data, each channel containing an 8-bit word which may represent a PCM-encoded analog/voice sample as provided by a codec (e.g., MITEL’s MT8964).

This serial input word is converted into parallel data and stored in the 256 X 8 Data Memory . Locations in the Data Memory are associated with particular channels on particular ST-BUS input streams. These locations can be read by the microprocessor which controls the chip.

Locations in the Connection 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 or it can originate from the microprocessor. If the data is switched from an input, then the contents of the Connection Memory Low location associated with the output channel is used to address the Data Memory. This Data Memory address corresponds to the channel on the input ST-BUS stream on which the data for switching arrived. If the data for the output channel originates from the microprocessor (Message Mode), then the contents of the Connection Memory Low location associated with the output channel are output directly, and this data is output repetitively on the channel once every frame until the microprocessor intervenes.

The Connection Memory data is received, via the Control Interface, at D7 to D0. The Control Interface also receives address information at A5 to A0 and handles the microprocessor control signals CS, DTA, R/W and DS. There are two parts to any address in the Data Memory or Connection Memory.

A5 A4 A3 A2 A1 A0 HEX ADDRESS LOCATION

0 1 1

•

* Writing to the Control Register is the only fast transaction.

†

Memory and stream are speciﬁed by the contents of the Control Register.

2-6

X 0 0

•

X 0 0

•

0 0

•

X 0 0

•

X 0 1

•

Figure 3- Address Memory Map

00 - 1F

20 21

•

Control Register *

Channel 0 Channel 1

Channel 31

† †

•

†

MT8980D

The higher order bits come from the Control Register, which may be written to or read from via the Control Interface. The lower order bits come from the address lines directly.

The Control Register also allows the chip to broadcast messages on all ST-BUS outputs (i.e., to put every channel into Message Mode), or to split the memory so that reads are from the Data Memory and writes are to the Connection Memory Low. The Connection Memory High determines whether individual output channels are in Message Mode, and allows individual output channels to go into a high-impedance state, which enables arrays of MT8980s to be constructed. It also controls the CSTo pin.

All ST-BUS timing is derived from the two signals C4i and F0i.

Software Control

The address lines on the Control Interface give access to the Control Register directly or, depending on the contents of the Control Register, to the High or Low sections of the Connection Memory or to the Data Memory.

If address line A5 is low, then the Control Register is addressed regardless of the other address lines (see Fig. 3). If A5 is high, then the address lines A4-A0 select the memory location corresponding to channel 0-31 for the memory and stream selected in the Control Register.

The data in the Control Register consists of mode control bits, memory select bits, and stream address bits (see Fig. 4). The memory select bits allow the Connection Memory High or Low or the Data Memory to be chosen, and the stream address bits deﬁne one of the ST-BUS input or output streams.

Bit 7 of the Control Register allows split memory operation - reads are from the Data Memory and writes are to the Connection Memory Low.

The other mode control bit, bit 6, puts every output channel on every output stream into active Message Mode; i.e., the contents of the Connection Memory Low are output on the ST-BUS output streams once every frame unless the ODE pin is low. In this mode the chip behaves as if bits 2 and 0 of every Connection Memory High location were 1, regardless of the actual values.

(unused)

Mode

Control

Bits

76543210

Memory

Select

Bits

Stream

Address

Bits

BIT NAME DESCRIPTION

7 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. 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 Message

Mode

When 1, the contents of the Connection Memory Low are output on the Serial Output streams except when the ODE pin is low. When 0, the Connection Memory bits for each channel determine what is output.

5 (unused)

4-3 Memory

Select Bits

0-0 - Not to be used 0-1 - Data Memory (read only from the microprocessor port) 1-0 - Connection Memory Low 1-1 - Connection Memory High

2-0 Stream

Address

Bits

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.

Figure 4 - Control Register Bits

2-7

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