HOST INTERFACE (HI)
5 - 58
PORT B
MOTOROLA
matically loads the DMA address counter from the HM1 and HM0 bits in the DMA
host to DSP mode. This DMA address is used with the HI to place the received
byte in the correct register (TXH, TXM, or TXL).
Figure 5-37 shows the differences between 24-, 16-, and 8-bit DMA data transfers. The
interrupt rate is three times faster for 8-bit data transfers than for 24-bit transfers. TXL is
always loaded last.
5.3.6.3.2
Host to DSP DMA Procedure
The following procedure outlines the typical steps that the host processor must take to
setup and terminate a host-to-DSP DMA transfer (see Figure 5-39).
HREQ
DMA
0
HF3
HF2
TRDY
TXDE RXDF
$2
7
0
INTERRUPT STATUS
REGISTER (ISR)
(READ ONLY)
0
0
Interrupt Mode (DMA Off)
0
1
24 Bit DMA Mode
1
0
16 Bit DMA Mode
1
1
8 Bit DMA Mode
INIT
HM1
HM0
HF1
HF0
0
TREQ RREQ
$0
7
0
MODES
DMA
0
0
HF1
HF0
HCP
HTDE
HRDF
X:$FFE9
7
0
HOST STATUS
REGISTER (HSR)
(READ ONLY)
TREQ
RREQ
HREQ PIN
0
0
No Interrupts (Polling)
0
1
RXDF Request (Interrupt)
1
0
XDE Request (Interrupt)
1
1
XDF and TXDE Request (Interrupts)
INTERRUPT CONTROL REGISTER (ICR)
(READ/WRITE)
TREQ
RREQ
HREQ PIN
0
0
No DMA
0
1
DSP to Host Request (RX)
1
0
Host to DSP Request (TX)
1
1
Undefined (Illegal)
INTERRUPT MODE (DMA OFF)
DMA MODE
Figure 5-38 Host Bits with TREQ and RREQ
RESET CONDITION
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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