Zilog Z16C35 Manual do Utilizador descarregar pdf (Página 80)

ISCC

User Manual

UM011002-0808

4.4.2 SDLC Receive

The receiver in the ISCC™ always searches the receive data stream for flag characters in

SDLC mode. Ordinarily, the receiver transfers all received data between flags to the

receive data FIFO. However, if the receiver is in Hunt mode no flag is received. The

receiver is in Hunt mode when first enabled, or the receiver may be placed in Hunt mode

by the processor issuing the Enter Hunt mode command in WR3. this bit (D4) is a com-

mand, and writing a “0” to it has no effect. The Hunt s

tatus of the receiver is reported by

the Sync/Hunt bit in RR0.

Sync/Hunt is one of the possible sources of external/status interrupts, with both transitions

causing an interrupt. This is

true even if the Sync/Hunt bit is set as a result of the processor

issuing the Enter Hunt mode command.

The receiver will automatically enter Hunt mode if

an abort is received. Because the

receiver al

ways searches the receive data stream for flags and automatically enters Hunt

Mode when an abort is received, the receiver will always handle frames correctly, and the

Enter Hunt Mode command should never be needed. The ISCC will drive the SYNC pin

Low to signal that a flag has been recognized. The timing for the SYNC signal is shown in

Figure 4-12.

The first byte in an SDLC frame is assumed by the

ISCC to be the address of the

second-

ary station for which the frame is intended. The ISCC provides several options for han-

dling this address.

WR10 7 Select CRC preset value

WR0 6-7 Reset Tx CRC

WR10 1 Abort/flag on underrun

WR0 6-7 Tx underrun

WR7 6-7 Flag

Table 4–19. Initializing the Transmitter in SDLC Mode

Page 74 of 316

1 2 ... 75 76 77 78 79 80 81 82 83 84 85 ... 321 322

Sem comentários

Zilog Z16C35 Manual do Utilizador Página 80