Z80 datasheet(248/330 Pages) ZILOG

248 / 330 page

<%27 2GTKRJGTCNU

7UGT /CPWCN

UM008101-0601

Serial Input/Output

228

routine in the memory. To service operations in both channels and to elimi-

nate the necessity of writing a status analysis routine, the Z80 SIO can

modify the interrupt vector in RR2 so that it points directly to one of eight

interrupt service routines. This is done under program control by setting a

program bit (WR1, D2) in Channel B called “Status Affects Vector.” when

this bit is set, the interrupt vector in WR2 is modified according to the

assigned priority of the various interrupting conditions. The table in “Write

Transmit interrupts, Receive interrupts, and External/ Status interrupts are

the main sources of interrupts (Figure 110). Each interrupt source is

enabled under program control with Channel A having a higher priority

than Channel B, and with Receiver, Transmit, and External/Status inter-

rupts prioritized in that order within each channel. When the Transmit

interrupt is enabled, the CPU is interrupted by the transmit buffer

becoming empty. This implies that the transmitter had a data character

written into it so it can become empty. When enabled, the receiver can

interrupt the CPU in one of three ways:

• Interrupt on first receive character

• Interrupt on all receive characters

• Interrupt on a Special Receive condition

Interrupt On First Character is typically used with the Block Transfer mode.

Interrupt On All Receive Characters has the option of modifying the inter-

rupt vector in the event of a parity error. The Special Receive Condition

interrupt can occur on a character or message basis, for example, End-of-

Frame interrupt in SDLC. The Special Receive condition can cause an

interrupt only if the Interrupt On First Receive Character or Interrupt On

All Receive Characters mode is selected. In Interrupt On First Receive

Character, an interrupt can occur from Special Receive conditions (except

Parity Error) after the first receive character interrupt, for example, Receive

Overrun interrupt.

The main function of the External/Status interrupt is to monitor the signal

transitions of the CTS,DCD,and SYNC pins; however, an External/Status

Z80 Datasheet(PDF) 248 Page - Zilog, Inc.