Host Side Registers
MOTOROLA
Host Interface Eight (HI8)
16-21
Preliminary
16
16.9.1.5 Host Flag 0 (HF0)—Bit 3
The Host Flag 0 (HF0) bit is used as a general purpose flag for Host-to-DSP
communication. The HF0 bit can be set or cleared by the Host Processor, but cannot be
changed by the DSP core. The HF0 bit is reflected in the HSR on the DSP Side. The HF0
bit is cleared on DSP reset.
16.9.1.6 ICR Host Little Endian (HLEND)—Bit 2
The Host Little Endian (HLEND) bit allows the HI8 to be accessed by the Host in or Big
Endian data order. When the HLEND bit is set, the HI8 can be accessed by the Host in
Little Endian order. The RXH/TXH is located at address $7 and RXL/TXL at $6. When
the HLEND bit is cleared, the HI8 can be accessed by the Host in Big Endian Host data
order. The RXH/TXH is located at address $6 and RXL/TXL at $7. The HLEND bit is
cleared on hardware reset.
16.9.1.7 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-DSP and enables the HREQ pin to request these data transfers.
16.9.1.8 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 register (ISR) is set. When RREQ is cleared, RXDF interrupts are
disabled. When RREQ is set, 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 DSP-to-Host, enabling the HREQ pin to request these data transfers. RREQ is
cleared by DSP reset.