HOST INTERFACE (HI)
5 - 26
PORT B
MOTOROLA
There are two methods of initialization: 1) allowing the DMA address counter to be auto-
matically set after transferring a word, and 2) setting the INIT bit, which sets the DMA
address counter. Using the INIT bit to initialize the HI hardware may or may not be nec-
essary, depending on the software design of the interface.
The type of initialization done when the INIT bit is set depends on the state of TREQ and
RREQ in the HI. The INIT command, which is local to the HI, is designed to conveniently
configure the HI into the desired data transfer mode. The commands are described in the
following paragraphs and in Table 5-4. The host sets the INIT bit, which causes the HI hard-
ware to execute the INIT command. The interface hardware clears the INIT bit when the
command has been executed. Hardware, software, individual, and STOP resets clear INIT.
INIT execution always loads the DMA address counter and clears the channel according
to TREQ and RREQ. INIT execution is not affected by HM1 and HM0.
The internal DMA counter is incremented with each DMA transfer (each HACK pulse) until
it reaches the last data register (RXL or TXL). When the DMA transfer is completed, the
counter is loaded with the value of the HM1 and HM0 bits. When changing the size of the
TREQ
RREQ
After INIT Execution
Transfer
Direction
Initialized
Interrupt Mode (HM1 = 0, HM0 = 0) INIT Execution
0
0
INIT = 0; Address Counter = 00
None
0
1
INIT = 0; RXDF = 0; HTDE = 1; Address
Counter = 00
DSP to Host
1
0
INIT = 0; TXDE = 1; HRDF = 0; Address
Counter = 00
Host to DSP
1
1
INIT = 0; RXDF = 0; HTDE = 1; TXDE =
1; HRDF = 0; Address Counter = 00
Host to/from DSP
DMA Mode (HM1 or HM0 = 1) INIT Execution
0
0
INIT = 0; Address Counter = HM1, HM0
None
0
1
INIT = 0; RXDF = 0; HTDE = 1; Address
Counter = HM1, HM0
DSP to Host
1
0
INIT = 0; TXDE = 1; HRDF = 0; Address
Counter = HM1, HM0
Host to DSP
1
1
Undefined (Illegal)
Undefined
Table 5-4 HREQ Pin Definition
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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