HOST INTERFACE (HI)
MOTOROLA
PORT B
5 - 27
DMA word (changing HM0 and HM1 in the ICR), the DMA counter is not automatically
updated, and, as a result, the DMA counter will point to the wrong data register immedi-
ately after HM1 and HM0 are changed. The INIT function must be used to preset the
internal DMA counter correctly. Always set INIT after changing HM0 and HM1. However,
the DMA counter can not be initialized in the middle of a DMA transfer. Even though the
INIT bit is set, the internal DMA controller will wait until after completing the data transfer
in progress before executing the initialization.
5.3.3.3
Command Vector Register (CVR)
The host processor uses the CVR to cause the DSP to execute a vectored interrupt. The
host command feature is independent of the data transfer mechanisms in the HI. It can
be used to cause any of the 64 possible interrupt routines in the DSP CPU to be exe-
cuted. The command vector register is shown in Figure 5-14.
5.3.3.3.1
CVR Host Vector (HV) Bits 0–5
The six HV bits select the host command exception address to be used by the host com-
mand exception logic. When the host command exception is recognized by the DSP
interrupt control logic, the starting address of the exception taken is 2
×
HV. The host can
write HC and HV in the same write cycle, if desired.
The host processor can select any of the 64 possible exception routine starting addresses
in the DSP by writing the exception routine starting address divided by 2 into HV. This
means that the host processor can force any of the existing exception handlers (SSI, SCI,
IRQA, IRQB, etc.) and can use any of the reserved or otherwise unused starting
addresses provided they have been preprogrammed in the DSP. HV is set to $12 (vector
location $0024) by hardware, software, individual, and STOP resets. Vector location
$0024 is the first of 45 special host command vectors.
HOST VECTOR
RESERVED
HOST COMMAND
HV1
HV0
HV2
HV3
HV4
HV5
*
HC
0
7
6
5
4
3
2
1
Figure 5-14 Command Vector Register
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Freescale Semiconductor, Inc.
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