HOST INTERFACE (HI)
MOTOROLA
PORT B
5 - 23
Table 5-2 summarizes the effect of RREQ and TREQ on the HREQ pin.
5.3.3.2.3
ICR Reserved Bit (Bit 2)
This bit, which is reserved and unused, reads as a logic zero.
5.3.3.2.4
ICR Host Flag 0 (HF0) Bit 3
The HF0 bit is used as a general-purpose flag for host-to-DSP communication. HF0 may
be set or cleared by the host processor and cannot be changed by the DSP. HF0 is visi-
ble in the HSR on the DSP CPU side of the HI (see Figure 5-10). Hardware, software,
individual, and STOP resets clear HF0.
5.3.3.2.5
ICR Host Flag 1 (HF1) Bit 4
The HF1 bit is used as a general-purpose flag for host-to-DSP communication. HF1 may
be set or cleared by the host processor and cannot be changed by the DSP. Hardware,
software, individual, and STOP resets clear HF1.
5.3.3.2.6
ICR Host Mode Control (HM1 and HM0 bits) Bits 5 and 6
The HM0 and HM1 bits select the transfer mode of the HI (see Table 5-3). HM1 and HM0
enable the DMA mode of operation or interrupt (non-DMA) mode of operation.
When both HM1 and HM0 are cleared, the DMA mode is disabled, and the TREQ and
RREQ control bits are used for host processor interrupt control via the external HREQ out-
TREQ
RREQ
HREQ Pin
Interrupt Mode
0
0
No Interrupts (Polling)
0
1
RXDF Request (Interrupt)
1
0
TXDE Request (Interrupt)
1
1
RXDF and TXDE Request (Interrupts)
DMA Mode
0
0
No DMA
0
1
DSP to Host Request (RX)
1
0
Host to DSP Request (TX)
1
1
Undefined (Illegal)
Table 5-2 HREQ Pin Definition
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Freescale Semiconductor, Inc.
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