HOST INTERFACE (HI)
MOTOROLA
PORT B
5 - 15
5.3.2.1.5
HCR Host Flag 3 (HF3) Bit 4
The HF3 bit is used as a general-purpose flag for DSP-to-host communication. HF3 may
be set or cleared by the DSP. HF3 is visible in the ISR on the host processor side (see
Figure 5-10). Hardware and software resets clear HF3.
Note:
There are four host flags: two used by the host to signal the DSP (HF0 and HF1)
and two used by the DSP to signal the host processor (HF2 and HF3). They are
general purpose flags and are not designated for any specific purpose. The host
flags do not cause interrupts; they must be polled to see if they have changed.
These flags can be used individually or as encoded pairs. See
Host Port Usage Considerations – DSP Side
for additional information. An ex-
ample of the usage of host flags is the bootstrap loader, which is listed in the
DSP56001 Technical Data Sheet
. Host flags are used to tell the bootstrap program
whether or not to terminate early.
5.3.2.1.6
HCR Reserved Control (Bits 5, 6, and 7)
These unused bits are reserved for future expansion and should be written with zeros for
upward compatibility.
5.3.2.2
Host Status Register (HSR)
The HSR is an 8-bit read-only status register used by the DSP to interrogate status and
flags of the HI. It can not be directly accessed by the host processor. When the HSR is
read to the internal data bus, the register contents occupy the low-order byte of the data
bus; the high-order portion is zero filled. The status bits are described in the following
paragraphs.
5.3.2.2.1
HSR Host Receive Data Full (HRDF) Bit 0
The HRDF bit indicates that the host receive data register (HRX) contains data from the
host processor. HRDF is set when data is transferred from the TXH:TXM:TXL registers
to the HRX register. HRDF is cleared when HRX is read by the DSP. HRDF can also be
cleared by the host processor using the initialize function. Hardware, software, individual,
and STOP resets clear HRDF.
5.3.2.2.2
HSR Host Transmit Data Empty (HTDE) Bit 1
The HTDE bit indicates that the host transmit data register (HTX) is empty and can be written
by the DSP. HTDE is set when the HTX register is transferred to the RXH:RXM:RXL regis-
ters. HTDE is cleared when HTX is written by the DSP. HTDE can also be set by the host
processor using the initialize function. Hardware, software, individual, and STOP sets HTDE.
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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