HOST INTERFACE (HI)
MOTOROLA
PORT B
5 - 11
Interface – Host Side
Mapping:
Eight Consecutive Memory Locations
Memory-Mapped Peripheral for Microprocessors, DMA Controllers, etc.
Data Word: Eight Bits
Transfer Modes:
DSP to Host
Host to DSP
Host Command
Mixed 8-, 16-, and 24-Bit Data Transfers
Handshaking Protocols:
Software Polled
Interrupt Driven and Compatible with MC68000
Cycle Stealing DMA with Initialization
Dedicated Interrupts:
Separate Interrupt Vectors for Each Interrupt Source
Special host commands force DSP CPU interrupts under host processor control,
which are useful for:
Real-Time Production Diagnostics
Debugging Window for Program Development
Host Control Protocols and DMA Setup
Figure 5-8 is a block diagram showing the registers in the HI. These registers can be
divided vertically down the middle into registers visible to the host processor on the left
and registers visible to the DSP on the right. They can also be divided horizontally into
control at the top, DSP-to-host data transfer in the middle (HTX, RXH, RXM, and RXL),
and host-to-DSP data transfer at the bottom (THX, TXM, TXL, and HRX).
5.3.1
Host Interface – DSP CPU Viewpoint
The DSP CPU views the HI as a memory-mapped peripheral occupying three 24-bit
words in data memory space. The DSP may use the HI as a normal memory-mapped
peripheral, using either standard polled or interrupt programming techniques. Separate
transmit and receive data registers are double buffered to allow the DSP and host proces-
sor to efficiently transfer data at high speed. Memory mapping allows DSP CPU
communication with the HI registers to be accomplished using standard instructions and
addressing modes. In addition, the MOVEP instruction allows HI-to-memory and memory-
to-HI data transfers without going through an intermediate register. Both hardware and
software reset disable the HI and change Port B to general-purpose I/O with all pins des-
ignated as inputs.
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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