DSP56857 datasheet(448/662 Pages) FREESCALE

448 / 662 page

Host Side Registers

5685X Digital Signal Controller User Manual, Rev. 4

16-22

Freescale Semiconductor

16.9.1.6 ICR Transmit Request Enable (TREQ)—Bit 1

The Transmit Request Enable (TREQ) bit is used to control the HREQ pin for Host transmit data

transfers. In the Interrupt mode, and the DMA is off, TREQ is used to enable interrupt requests

via the external Host Request (HREQ or HTRQ) pin when the Transmit Data Register Empty

(TXDE) status bit in the Interrupt Status Register (ISR) is set. When TREQ is cleared, TXDE

interrupt is disabled. When TREQ is set, the external Host Request HREQ or HTRQ pin is

asserted if TXDE is set in the Interrupt mode.

In DMA modes, the TREQ must be set or cleared by software to select the direction of DMA

transfers. Setting TREQ sets the direction of the DMA transfer to be from Host-to-DSC and

enables the HREQ pin to request these data transfers.

16.9.1.7 Receive Request Enable (RREQ)—Bit 0

This bit is used to control the HREQ pin for Host receive data transfers. In the Interrupt mode

(HDMA off), the RREQ is used to enable interrupt requests via the external Host Request (HREQ

or HRRQ) pin when the Receive Data Register Full (RXDF) status bit in the Interrupt Status

the external Host Request HREQ pin or HRRQ is asserted if RXDF is set in interrupt mode.

In HDMA modes, the RREQ bit must be set or cleared by software to select the direction of

DMA transfers. Setting the RREQ bit sets the direction of the HDMA transfer to be from the

DSC-to-Host, enabling the HREQ pin to request these data transfers. RREQ is cleared by DSC

reset.

Table 16-10,Table 16-11, and Table 16-12 summarizes the effect of RREQ and TREQ on the

HREQ/HTRQ and HACK/HRRQ pins. TREQ is cleared by DSC reset.

Table 16-10.

HREQ Pin Definition–Interrupt Mode (HRMS = 0, HM1 = HM0 = 0)

TREQ

RREQ

HREQ Pin

No interrupts (Polling)

RXDF Request (Interrupt)

TXDE Request (Interrupt)

RXDF and TXDE Request (Interrupt)

DSP56857 Datasheet(PDF) 448 Page - Freescale Semiconductor, Inc