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M46

Baseband Processor for GSM Applications

Conexant Systems 

Baseband Processor

M46

Table 7. Timer Mode Register Functions

Bit

Function

7

Enable/disable serial shifting in of data to the Serial In Buffer Register:

0 = disabled

1 = enabled

6

Enable/disable serial shifting out of data from the Serial Out Buffer Register:

0 = disabled

1 = enabled

5

Reserved. Set to “0” for normal operation

4:0 N/A (reserved)

Precision Timing Generators (PTGs)____________________

PTG A generates symbol timing for the Serial Data Services

(SDS) port. PTG B generates symbol timing for the Debug Port.

Both timers can also generate an interrupt to the device

Interrupt Controller. The timers use the 3.9 MHz system clock as

an input clock. The output from either PTG is a clock signal at a

frequency that is calculated as follows:

Latch Value

Clock Frequency = Input Clock Frequency ×

65536

The input clock frequency is 3.9 MHz and the latch value is a

16-bit word that is individually programmable for each PTG.

For example, if a serial port baud rate of 230.4 kbps is required,

the port needs to be clocked at 16 times this rate which is

3.6864 MHz. Setting the latch value to 0xF1FA results in a PTG

output frequency of 3.686421 MHz, which is the closest to the

required frequency that the PTG can generate.

PTG Registers. The address and default values for the

Precision Timing Generator (PTG) Registers are specified in

Table 2. The PTG Registers each contain a Mode Register and

a Latch Register.

Mode Register. Each PTG has a dedicated Mode Register. The

Mode Register configures the operation of the PTG. The

function of each bit in the register is described in Table 8.

Latch Register. Each PTG has a dedicated Latch Register. The

latch value is programmed by writing to the Latch Register. The

latch value sets the PTG clock frequency.

Serial Ports

The BP device provides two asynchronous, full duplex serial

ports:

• Debug Port. This port is used to output protocol stack

signaling information and for remote control of the handset.

• Serial Data Services (SDS) Port. This port is used to

communicate with a data terminal or PC.

Both ports can operate at baud rates of up to 230.4 kbps.

Timing for the port is generated by two precision timers which, in

turn, derive their timing from the 3.9 MHz system clock.

The timing of both ports is RS-232-compatible. Since the BP is a

2.8 V device, the logic levels are not RS-232 compatible.

Therefore, external voltage translation circuitry is required to

interface either of the ports to an RS-232 interface on a PC.

Debug Port _________________________________________

There are two Debug Port signals:

• DEBUG_TX (transmit data output from the device)

• DEBUG_RX (receive data input to the device)

The serial port sends signaling information from the protocol

stack to monitor handset operation on a PC. The serial port

receives data from a PC to allow remote control of the handset

by the PC (e.g., originate a call, terminate a call, etc).

The Serial Port Registers are used to program the operating

mode and data rate of the Debug Port.

SDS Port ___________________________________________

There are two SDS Port signals:

• SDS_TX (transmit data)

• SDS_RX (receive data)

SDS timing is generated by Precision Timing Generator (PTG)

A. The clock to the interface circuitry is normally off (to save

power). When a start bit is seen on the SDS_RX signal or a byte

is written to the port output buffer, the clock is turned on.

The Serial Port Registers are used to program the operating

mode and data rate of the SDS Port.

100779C

Conexant

Proprietary Information and Specifications are Subject to Change

17

June 14, 2000

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