CD1284 datasheet(68/176 Pages) INTEL

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CD1284 — IEEE 1284-Compatible Parallel Interface Controller

Datasheet

• If there is no more data in the FIFO following the send break command, the break continues

indefinitely until terminated by a stop break command.

• If there is an insert delay command (see the next command) immediately following the send

break command, the break duration is set by the value programmed in the delay command.

Any other character in the FIFO immediately following the send break command carries an

‘implied’ end-of-break condition, causing the break to be terminated and the next character to

be sent.

NUL x’82 x’xx – Insert Delay

This command causes a delay between the previous character transmitted and the next character to

be transmitted. The hex value contained in the third byte of the sequence determines the time of the

delay based on the basic time period set by the PPR. The value is treated as an unsigned binary

value loaded into an internal counter. The counter decrements once for each tick of the prescale

period timer. Thus, if the PPR sets a basic timing period of 10 ms and the value set by the command

is 100 (x’64), then a delay of 1 second is generated. Multiple insert delay commands can be placed

in the FIFO if time delays longer than that generated by a single delay period are needed.

This command is useful when a delay is required after sending a carriage return. A printer is an

example of this type of situation. Often, the carriage return causes the printer to start a print cycle

and the sending device must wait for the print to complete before sending the next line of text

(unbuffered input). Using the insert delay command allows the delay to be performed

automatically without the need for the CPU to time it. The delay command is placed in the FIFO

directly following the carriage return and preceding the first data for the next line. The CD1284

automatically executes the delay following the carriage return, then restarts sending characters.

Another useful application of the delay command is as a built-in timer that the CPU uses as an

interrupt source causing it to periodically check its internal buffers for data to transmit. This

assumes that the channel is not currently transmitting data. When the CPU services the transmit

FIFO service request after a delay timeout (as set by the delay value) it can start transmission of a

buffer if data is available or resend the insert delay command and wait for the next service request.

An internal timer interrupt set by the CPU is now unnecessary to perform this function.

NUL x’83 – Stop BREAK

This command terminates a break in progress regardless of other conditions. This command can be

preceded by insert delay commands to set a specific, programmed break period if more than one

character time is required. Any character in the FIFO causes the break to terminate. NUL x’83 is

required only if it is necessary to stop the break and there is no more data to be sent. A break

continues until another character is sent or ESC x’83 is encountered in the FIFO.

NUL x’01–x’3F – Send Repeat Space

This command causes the CD1284 to send repeated space characters. The character following

NUL is interpreted as a binary count specifying the number of ASCII space (x’20) characters to

send. The count must be in the range of x’01 through x’3F (1–63 decimal).

5.8.3

Send Special Character Command

One command of the CD1284 transmits any one of the four special characters programmed in

SCHR1–SCHR4. The command is issued by the CCR[5] set to ‘1’, and the least-significant three

bits encoding a selection of one of the four characters. This function is preemptive, meaning that

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