HOST INTERFACE (HI)
MOTOROLA
PORT B
5 - 29
provides valid status so that polling techniques may be used by the host processor.
Hardware, software, individual, and STOP resets clear RXDF.
5.3.3.4.2
ISR Transmit Data Register Empty (TXDE) Bit 1
The TXDE bit indicates that the transmit byte registers (TXH, TXM, 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 byte low (TXL)
register is written by the host processor. TXL is normally the last byte of the transmit byte
registers to be 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 that polling techniques may be used by the host processor. Hardware,
software, individual, and STOP resets set TXDE.
5.3.3.4.3
ISR Transmitter Ready (TRDY) Bit 2
The TRDY status bit indicates that both the TXH,TXM,TXL and the HRX registers are empty.
TRDY=TXDE
•
HRDF
When TRDY is set to one, the data that the host processor writes to TXH,TXM, and TXL
will be immediately transferred to the DSP CPU side of the HI. This has many applica-
tions. For example, if the host processor issues a host command which causes the DSP
CPU to read the HRX, the host processor can be guaranteed that the data it just trans-
ferred to the HI is what is being received by the DSP CPU.
Hardware, software, individual, and STOP resets set TRDY.
5.3.3.4.4
ISR Host Flag 2 (HF2) Bit 3
The HF2 bit in the ISR indicates the state of host flag 2 in the HCR on the CPU side. HF2
can only be changed by the DSP (see Figure 5-10). HF2 is cleared by a hardware or
software reset.
5.3.3.4.5
ISR Host Flag 3 (HF3) Bit 4
The HF3 bit in the ISR indicates the state of host flag 3 in the HCR on the CPU side. HF3
can only be changed by the DSP (see Figure 5-10). HF3 is cleared by a hardware or
software reset.
5.3.3.4.6
ISR Reserved Bit (Bit 5)
This status bit is reserved for future expansion and will read as zero during host proces-
sor read operations.
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Freescale Semiconductor, Inc.
For More Information On This Product,
Go to: www.freescale.com
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