Zilog Z16C30 Manuel d'utilisateur télécharger pdf (Page 151)

7-23

Z16C30 USC

USER'S MANUAL

ZILOG

UM97USC0100

The Vector Includes Status field (VIS; ICR12-9) controls

whether the vector, that the channel returns during an

interrupt acknowledge cycle in which the highest-priority

requesting type is in the channel, identifies the type or not.

Such vector modification can be enabled for all types in the

channel, or only for those above a selected priority level:

VIS Which types appear in vectors

0xxx No types

100x All types

1010 IOP and above (not Misc)

1011 Transmit Data and above

1100 Transmit Status and above

1101 Receive Data & Status

1110 Receive Status only

1111 No types

If the contents of VIS allow the highest-priority type, that’s

requesting at the time of an Interrupt Acknowledge cycle,

to modify the interrupt vector, then bits 3-1 of the returned

vector identify that type as described in the next section.

If not, the channel returns the 8-bit vector exactly as the

host software programmed it.

7.15 INTERRUPT VECTORS

Software can read and write a channel’s interrupt vector

information in the Interrupt Vector Register (IVR). This

returns during an interrupt acknowledge cycle in which the

highest priority requesting type is in the channel.

Figure 7-18 shows the IVR. The basic vector can be written

and read in its LSByte; software can read a modified

version of the vector in its MSByte. (Writing the MSByte has

no effect.) Bits 15-12 and 8 are the image of those in the

corresponding bits of the LSByte, while the TypeCode

field (IVR11-9) gives the identity of the highest priority

interrupt type that has its IP bit set (the state of its IUS bit

doesn’t matter).

TypeCode Meaning

000 No interrupt pending

001 Miscellaneous

010 I/O pin

011 Transmit Data

100 Transmit Status

101 Receive Data

110 Receive Status

111 (will not be read)

The state of the VIS field (ICR12-9) has no effect on reading

the IVR. VIS simply controls how the channel decides

whether to return IVR15-8 or IVR7-0 as the interrupt vector

when it responds to an interrupt acknowledge cycle.

UM009402-0201

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Zilog Z16C30 Manuel d'utilisateur Page 151

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