Servicing the Host Interface
MOTOROLA
Host Interface Eight (HI8)
16-25
Preliminary
16
mode is enabled and the Host Processor should not use the active DMA channel
(RXH:RXL or TXH:TXL depending on DMA direction) to avoid conflicts with the DMA
data transfers.
Note:
This bit is always 0 if HRMS = 1 in the Host Control Register because the
HREQ and HACK function is disabled, thereby disabling the Host DMA
operations.
16.10.1.4 Reserved Bit–Bit 5
This bit is reserved or not implemented. It is read as, and written with 0s.
16.10.1.5 Host Flag 3 (HF3)–Bit 4
The Host Flag 3 (HF3) bit in the Interrupt Status Register indicates the state of Host Flag 3
in the Host Control Register on the DSP Side. The HF3 bit can only be changed by the
16.10.1.6 Host Flag 2 (HF2)—Bit 3
The Host Flag 2 (HF2) bit in the Interface Control Register (ISR) indicates the state of
Host Flag 2 in the Host Control Register on the DSP Side. The HF2 bit can only be
16.10.1.7 Transmitter Ready (TRDY)—Bit 2
The Transmitter Ready (TRDY) flag bit indicates TXH, TXL, and the HRX registers are
empty. When the TRDY bit is set, the data the Host Processor writes to the TXH and TXL
registers is immediately transferred to the DSP Side of the HI8. The many applications can
use this feature. For example, if the Host Processor issues a Host Command causing the
DSP core to read the HRX, the Host Processor can be guaranteed the data is just
transferred to the HI8 is what is being received by the DSP core.
16.10.1.8 Transmit Data Register Empty (TXDE)—Bit 1
Setting the Transmit Data Register Empty (TXDE) bit indicates the transmit byte registers
(TXH, and TXL) are empty and can be written by the Host Processor. TXDE is set when
the transmit byte registers are transferred to the HRX register. TXDE is cleared when the
transmit (TXL or TXH according to HLEND bit) register is written by the Host Processor.
TXDE can be set by the Host Processor using the initialize feature. TXDE may be used to
assert the external HREQ pin if the TREQ bit is set. Regardless of whether the TXDE
interrupt is enabled, TXDE provides valid status so polling techniques may be used by the
Host Processor.