DSP56857 datasheet(445/662 Pages) FREESCALE

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Host Side Registers

Host Interface Eight (HI8), Rev. 4

Freescale Semiconductor

16-19

16.9.1.1 Initialize (INIT)—Bit 7

The Initialize (INIT) bit is used by the Host Processor to force initialization of the HI8 hardware.

Initialization consists of configuring the HI8 transmit and receive control bits. Using the INIT bit

to initialize the HI8 hardware may or may not be necessary, depending upon the software design

of the interface.

The type of initialization performed when the INIT bit is set depends on the state of TREQ and

RREQ bits located in the Interface Control Register. The INIT command, local to the HI8, is

designed to conveniently configure the HI8 into the desired data transfer mode. Those commands

are described in Figure 16-7. The Host Processor sets the INIT bit, causing the HI8 to execute

the INIT command. The interface hardware clears the INIT bit when the command has been

executed.

16.9.1.2 Host Mode Control (HM1, HM0)—Bits 6–5

The Host mode control bits HM0 and HM1 select the Transfer mode of the HI8. HM1 and HM0

enable the DMA mode of operation, or they interrupt a no-Host DMA mode of operation when

HREQ bit in the Host Control Register (HCR) is set.

When the Host DMA mode is enabled, the HREQ pin is used as a DMA transfer request output to

a Host DMA controller and the HACK pin is used as a DMA Transfer Acknowledge input from a

Table 16-7.

INIT Execution Definition–Interrupt Mode

TREQ

RREQ

After INIT Execution

Transfer Direction Initialized

INIT = 0

None

INIT = 0; RXDF = 0; HTDE = 1

DSC-to-Host

INIT = 0; TXDE = 1; HRDF = 0

Host-to-DSC

INIT = 0; RXDF = 0; HTDE = 1;TXDE = 1; HRDF = 0

Host-to/from-DSC

Table 16-8.

INIT Execution Definition–HDMA Mode (HM1 = 1)

TREQ

RREQ

After INIT Execution

Transfer Direction Initialized

INIT = 0; address counter = HM1, HM0

None

INIT = 0; RXDF = 0; HTDE = 1;

address counter = HM1, HM0

DSC-to-Host

INIT = 0; TXDE = 1; HRDF = 0;

address counter = HM1, HM0

Host -to-DSC

Undefined (illegal)

Host-to/from-DSC

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