Z80 datasheet(296/330 Pages) ZILOG

296 / 330 page

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UM008101-0601

Serial Input/Output

276

Command 4 (Enable Interrupt On Next Receive Character). If the Interrupt

On First Receive Character mode is selected, command 4 reactivates the

Enable Interrupt On Next Receive Character mode after receiving each

complete message. This sequence prepares the Z80 SIO for the next message.

Command 5 (Reset Transmitter Interrupt Pending). A transmitter interrupt

occurs when the transmit buffer becomes empty. This interrupt happens

only when the Transmit Interrupt Enable mode is selected. When there are

no more characters to be sent for example, at the end of message, issuing

this command prevents further transmitter interrupts until after the next

character is loaded to the transmit buffer or until CRC is completely sent.

Command 6 (Error Reset). This command resets the error latches. Parity

and Overrun errors are latched in RR1 until they are reset with this

command. Using this method, parity errors occurring in block transfers can

be examined at the end of the block.

Command 7 (Return From Interrupt). This command must be issued in

Channel A and is interpreted by the Z80 SIO in the same way it interprets

an RETI command on the data bus. This command resets the interrupt

under-service latch of the highest priority internal device under service.

This reset allows lower-priority devices to interrupt through the daisy-

chain. This command also allows use of the internal daisy-chain even in

systems with no external daisy-chain or RETI command.

CRC Reset Codes 0 and 1 (D6 and D7). Used together, these bits select one

of the three following reset commands, described in Table 14:

Z80 Datasheet(PDF) 296 Page - Zilog, Inc.