Zilog Z16C35 Manual de usuario descargar pdf (Pagina 55)

ISCC

User Manual

UM011002-0808

4.2 ASYNCHRONOUS MODE

In asynchronous communications data is transferred in the format shown in Figure 4-3.

Figure 4–18. Asynchronous Message Format

The transmission of a character begins when the line makes a transition from the “1”

state, or MARK condition to the “0” state or SPACE condition. This transition is the refer-

ence by which the character’s bit cell boundaries are defined. Though the transmitter an

receiver have no common clock signal, there must be an agreement as to the data rate so

that the receiver can always sample the data in the center of the bit cell.

The character can be broken up into four fields:

8. Start bit - signals the beginning of a character frame.

9. Data field - typi

cally 5-8 bits wide.

10. Parity bit - optional, provides mechanism for checking character validity, transmitter

and receiver agree that:

11. Data + Parity bit contains odd number of 1s (odd parity) or Data + Parity bit contains

even number of 1s (even parity).

Stop bit(s) - provides a minimum interval betwee

n the end of one chara

cter and the begin-

ning of the next.

The ISCC™ supports Asynchronous mode with a number of programmable options

including the number of bits per character, the nu

mber of stop bits, the clock factor,

modem interface signals and break detect and generation.

Asynchronous mode is selected by programming the desired number of stop bits in D3 and

D2 or WR4. Programming these two bits with other th

an “00” places both the receiver and

transmitter in Asynchronous mode. In this mode, the ISCC ignores the state of bits D4,

D3, and D2 of WR3, bits D5 and D4 of WR4, bits D2 and D0 of WR5, all of WR6 and

Idle State

of Line

LSB

Start

Bit

Parity

Bit

Data Field

Stop

Bit(s)

1.5

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Zilog Z16C35 Manual de usuario Pagina 55

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