SCD1284 datasheet(93/176 Pages) INTEL

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IEEE 1284-Compatible Parallel Interface Controller — CD1284

Datasheet

6.2.2

Global Function Initialization

Once chip reset has been completed, the next step is to set the Global Operating mode and timer

prescale. All other initialization occurs at the channel level.

Set the Prescaler Period Register (PPR)

The PPR sets the master time ‘tick’ for the CD1284. It is a binary value that sets a constant by

which the system clock is divided (after a fixed prescale of 512) to produce the internal clock for

the on-chip timers (This does not include baud rate generators). This clock is used for receiver

FIFO time-out generation and delay timing for the insert delay command in the embedded transmit

command set. For example, to generate a timer clock of 1 ms, the value is computed as:

The value 49 is loaded into the PPR. This value, selects an approximate 1-kHz clock as the source

for the RTPR (Receiver Time-out Period registers) of each channel. Those registers are loaded with

an appropriate value divisor that generate the desired character time-out periods. This value, 49, is

the recommended minimum value that is placed in the PPR for a clock frequency of 25 MHz.

Values that generate a time period of less than 1 ms adversely affect the performance of the MPU,

and thus, overall serial data performance.

6.2.3

Serial Channel Initialization

At this point, the basic operation of the CD1284 serial channels are set up. The internal register

states are cleared and basic timer operations are initialized. The next step is programming the

operating modes of each channel. This includes setting the values for the interrupt vectors, the

receive and transmit baud rates, number of bits per character, number of stop bits, parity, special

characters, if any, and so on. Each channel can have a completely unique set of operating

characteristics or they can all be the same.

Serial channel initialization is application-dependent. The operating modes of one channel have no

effect on the operation of others.

The following code, is a typical initialization sequence for setting up a single serial channel:

9600 baud, send and receive

8 bits per character, 1 stop bit,No parity

Automatic In-Band (Xon/Xoff) flow control

Transparent flow control

Special character detect enabled

Eight character receive FIFO threshold

Receiver and transmitter enabled for interrupt operation

Enable ISTRIP on incoming characters

A clear way of showing this initialization sequence is by a ‘C’ program fragment; the code shown

below, is compatible with Borland Turbo C

:

/* Init channel. Channel number is included in call. Register names and addresses

are defined in the header file (not shown). This routine does not include parallel

channel initialization. */

init_channel(chan)

char

chan

{

25MHz

512

------------------





1ms

48.828

SCD1284 Datasheet(PDF) 93 Page - Intel Corporation

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