MT8924

Preliminary Information

8-4

Figure 2 - Pin Connections

Pin Description

Pin #

Name

Description

1TD

Tone Duration (Input). When TD is High, a PCM-coded tone is sent out to all channels of

the enabled conferences instead of PCM data. TD is latched by frame pulse F0i so that all

channels have the same tone during the same frame number. When TD is Low, normal

operation is enabled.

2TF

Tone Frequency (Input). This input is connected to an external squarewave generator. TF

is strobed by frame pulse F0i so that all channels have the same tone frequency during the

same number of frames. The PCM-coded tone level corresponds to 1/10th of the full scale

value, and is activated when TD is High.

3

RESET

Master RESET (Input). This input is used for system initialization after power up, or when

the companding law format has been changed. The RESET pin is strobed by the rising edge

of clock Cki. Complete circuit initialization takes two frame periods. Initialization disables the

output drivers of the microprocessor interface and DSTo.

4OS

Overflow Signalling (Output). When OS is Low, a conference is in the overflow condition.

This signal is delayed by half of a timeslot relative to the beginning of the output channel of

the conference in overflow (see Figure 9).

ST-BUS Serial Output. This pin is the output for the PCM signal. It is enabled upon

channel selection, otherwise it is placed in a high impedance state. Maximum bit rate is

2.048 Mb/s.

6-13

D7 to D0 Data Bus I/O Port. These are bidirectional data pins over which data and instructions are

transferred to and from the microprocessor (where D0 is the least significant bit). The bus is

in a high impedance state when RESET is Low and/or CS is High.

14

Positive Supply Voltage. Nominally 5 volts.

15

C/D

Control/Data Select (Input). The signal on this input defines whether the information on the

data bus should be interpreted as opcode or data. During a write operation a Low signal

defines the bus content as data, while a High signal defines it as opcode. During a read

operation this input differentiates overflow status between the first eight channels for C/D

being LOW, and the last two channels for C/D being HIGH (see Instruction 4). This input also

allows status monitoring (see Instruction 6) during a read operation.

16

CS

Chip Select (Input). This active low input selects the device for microprocessor read/write

operations. When CS is Low, data and instructions can be transferred to or from the

microprocessor, and when CS is High, the data bus is in a high impedance state.

17

RD

Read (Input).

This active low input is for the read signal on the microprocessor interface.

The data bus is updated on the falling edge of RD.

18

WR

Write Input. This active low input is for the write signal on the microprocessor interface. The

data bus is strobed on the rising edge of WR.

1

2

3

4

5

6

7

8

9

10

11

12

13

14

15

16

24

23

22

21

20

19

18

17

TD

TF

RESET

OS

D7

D6

D4

D3

D2

D1

VSS

A/

µ

DSTi

Cko

Cki

F0i

WR

RD

CS

C/D

VDD

D0

DSTo

D5