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Host Interface (HI08)

DSP56321 Technical Data, Rev. 11

Freescale Semiconductor

1-7

1.6 Host Interface (HI08)

The HI08 provides a fast, 8-bit, parallel data port that connects directly to the host bus. The HI08 supports a variety

of standard buses and connects directly to a number of industry-standard microcomputers, microprocessors, DSPs,

and DMA hardware.

1.6.1

Host Port Usage Considerations

Careful synchronization is required when the system reads multiple-bit registers that are written by another

asynchronous system. This is a common problem when two asynchronous systems are connected (as they are in the

Host port). The considerations for proper operation are discussed in Table 1-9.

1.6.2

Host Port Configuration

HI08 signal functions vary according to the programmed configuration of the interface as determined by the 16 bits

in the HI08 Port Control Register.

Table 1-9.

Host Port Usage Considerations

Action

Description

Asynchronous read of receive byte

registers

When reading the receive byte registers, Receive register High (RXH), Receive register Middle

(RXM), or Receive register Low (RXL), the host interface programmer should use interrupts or poll

the Receive register Data Full (RXDF) flag that indicates data is available. This assures that the data

in the receive byte registers is valid.

Asynchronous write to transmit byte

registers

The host interface programmer should not write to the transmit byte registers, Transmit register High

(TXH), Transmit register Middle (TXM), or Transmit register Low (TXL), unless the Transmit register

Data Empty (TXDE) bit is set indicating that the transmit byte registers are empty. This guarantees

that the transmit byte registers transfer valid data to the Host Receive (HRX) register.

Asynchronous write to host vector

The host interface programmer must change the Host Vector (HV) register only when the Host

Command bit (HC) is clear. This practice guarantees that the DSP interrupt control logic receives a

stable vector.

Table 1-10.

Host Interface

Signal Name

Type

State During

Reset1,2

Signal Description

H[0–7]

HAD[0–7]

PB[0–7]

Input/Output

Input or Output

Ignored Input

Host Data—When the HI08 is programmed to interface with a non-multiplexed

host bus and the HI function is selected, these signals are lines 0–7 of the

bidirectional Data bus.

Host Address—When the HI08 is programmed to interface with a multiplexed

host bus and the HI function is selected, these signals are lines 0–7 of the

bidirectional multiplexed Address/Data bus.

Port B 0–7—When the HI08 is configured as GPIO through the HI08 Port

Control Register, these signals are individually programmed as inputs or outputs

through the HI08 Data Direction Register.

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