Host Side Registers
MOTOROLA
Host Interface Eight (HI8)
16-17
Preliminary
16
The CVR is a special command register used by the Host Processor to issue commands to
the DSP. Each of these registers can be accessed only by the Host Processor.
Standard Host Processor instructions such as byte move and addressing modes are used to
communicate with the HI8 registers. The HI8 registers are addressed allowing 8-bit Host
Processors to use 8/16-bit load and store instructions for data transfers. The HREQ /
HTRQ and HACK / HRRQ handshake flags are provided for polled or interrupt driven
data transfers with the Host Processor. Because the DSP interrupt response is sufficiently
rapid, most host microprocessors can load or store data at their maximum programmed I/O
instruction rate without testing the handshake flags for each transfer. If full handshake is
not needed, the Host Processor can treat the DSP as a fast device, allowing data to be
transferred between the Host Processor and the DSP at the fastest Host Processor data rate.
One of the most innovative features of the HI8 is the Host Command feature. With this
feature, the Host Processor can issue vectored interrupt requests to the DSP core. The Host
can select any of 128 DSP interrupt routines to be executed by writing a vector address
register in the HI8. This flexibility allows the Host programmer to execute as many as 128
pre-programmed functions inside the DSP core. For example, Host Interrupts permits the
Host Processor to read or write DSP registers (data or program memory locations), force
interrupt handlers (i.e., ESSI, SCI, IRQA and IRQB interrupt routines) to perform control
and debugging operations when interrupt routines are implemented in the DSP to perform
these tasks.
Note:
Please be aware when the DSP core enters the Stop mode, the HI8 pins are
electrically disconnected internally, thus disabling the HI8 until the core leaves
Stop mode. While the HI8 configuration remains unchanged in Stop mode, the
core cannot be restarted via the HI8 interface.
Do not issue a STOP command to the DSP via the HI8 unless some other
mechanism for exiting Stop mode is provided.
Table 16-7.
HI8 Host Side Register Map
Register Name
Address
Offset
Big Endian
HLEND = 0
Little Endian
HLEND = 1
Interface Control
0
ICR
Command Vector
1
CVR
Interface Status
2
ISR
Interrupt Vector
3
IVR
Unused
4
00000000
Unused
5
00000000
Receive/Transmit
Bytes
6
RXH/TXH
RXL/TXL
7
RXL/TXL
RXH/TXH