DSP56857 datasheet(441/662 Pages) FREESCALE

441 / 662 page

DSC Side Registers

Host Interface Eight (HI8), Rev. 4

Freescale Semiconductor

16-15

16.8.3 HI8 Transmit Data Register (HTX)

The HI8 Transmit Data (HTX) register is used for DSC-to-Host data transfers. The HTX register

is viewed as a 16-bit write-only register by the DSC core. Writing to the HTX register clears the

HTDE bit in the HSR. The DSC can program the HTIE bit causing a Host Transmit Data inter-

rupt when the HTDE bit is set. The HTX register is transferred as 16-bit data to the receive byte

registers RXH/RXL when both the HTDE bit on the DSC Side and the RXDF status bits on the

Host Side are cleared. This transfer operation sets both RXDF and HTDE bits. Data should not be

written to the HTX register until the HTDE bit is set to prevent the previous data from being

overwritten.

Figure 16-7. HI8 Transmit Data Register (HTX)

See Programmer’s Sheet on Appendix page B - 139

16.8.4 HI8 Receive Data Register (HRX)

The HI8 Receive Data (HRX) register is used for Host-to-DSC data transfers. The HRX register

is viewed as a 16-bit read-only register by the DSC core. The HRX register is loaded with 16-bit

data from the Transmit Data registers TXH/TXL on the Host Side when both the Transmit Data

registers empty TXDE on the Host Side, and DSC Host Receive Data Full (HRDF) bits are

cleared. This transfer operation sets TXDE and HRDF bits. The HRX register contains valid data

when the HRDF bit is set. Reading HRX clears HRDF. The DSC may program the HRIE bit to

cause a Host Receive Data interrupt when HRDF is set.

Figure 16-8. HI8 Receive Data Register (HRX)

See Programmer’s Sheet on Appendix page B - 139

16.8.5 DSC Side Registers After Reset

Table 16-6 shows the results of the three reset types on the bits in each of the HI8 registers

accessible by the DSC core.

Base + $2

Read

Write

HIGH BYTE (FROM HRX)

LOW BYTE (FROM LRX)

Reset

000

000000

Base + $2

Read

HIGH BYTE (FROM HTX)

LOW BYTE (FROM LTX)

Write

Reset

000

000000

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