MK68564 datasheet(17/46 Pages) STMICROELECTRONICS

17 / 46 page

Control Register, Interrupt Control Register, Recei-

ver Control Register, Transmitter Control Register,

Sync Word 1, and Sync Word 2. The Mode Control

ters to assure proper operation of the SIO. The fol-

lowing

registers are used to transfer data or

communicate status between the SIO and the CPU

or other bus master : Command Register, Status

the Vector Register.

The SIO provides four I/O lines in Synchronous

modes that may be used for modem control, for ex-

ternal interrupts, or as general purpose I/O. The Re-

quest To Send (RTS) and Data Terminal Ready

(DTR) pins are outputs that follow the inverted state

of their respective bits in the Transmit Control Re-

gister. The Data Carrier Detect (DCD) and Clear To

Send (CTS) pins are inputs that can be used as auto

enables to the receiver and transmitter, respective-

ly. If External/Status Interrupts are enabled, the

DCD and CTS pins will be monitored for a change

of status. If these inputs change for a period of time

greater than the minimum specified pulse width, an

interrupt will be generated.

In the following discussion, all interrupt modes are

assumed enabled.

SYNCHRONOUS TRANSMIT

Initialization. Byte-oriented transmitter programs

are usually initialized with the following parameters :

odd-even or no parity, x1 clock mode, 8- or 16-bit

sync character(s), CRC polynomial, Transmit En-

ables, interrupt modes, and transmit character

length. If Parity is enabled, the transmitter will only

add a parity bit to a character that is loaded into the

transmit buffer ; it will not add a parity bit to the auto-

matically inserted sync character(s) or the CRC

characters.

One of two polynomials may be used with Synchro-

nous modes, CRC-16 (X

16 +X15 +X2 +1) or SDLC-

CRC (X

16 +X12 +X5 + 1). For either polynomial

(SDLC mode not selected), the CRC generator and

checker are reset to all zeros. Both the receiver and

transmitter use the same polynomial.

After reset (hardware or software), or when the

transmitter is not enabled, the Transmit Data (TxD)

output pin is held High (marking). Under program

control, the Send Break bit in the Transmitter Control

pin to a Low level (spacing), even if the transmitter

is not enabled. The spacing condition will persist un-

til the Send Break bit is reset to a zero. A program-

med break is effective as soon as it is written into the

Transmit Control Register ; any characters in the

transmit buffer and transmit shift register are lost.

If the transmit buffer is empty when the Transmit En-

able bit is set to a one, the transmitter will start sen-

ding 8- or 16-bit sync characters. Continuous syncs

will be transmitted on the TxD output pin, as long as

no data is loaded into the transmit buffer. Note, if a

Figure 10 : Synchronous Formats.

V000383

MK68564

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