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Table 6-17. Interface Status Register (ISR) Bit Definitions (Continued)
Bit Number
Bit Name
0
RXDF
6.7.4 Interrupt Vector Register (IVR)
The IVR is an 8-bit read/write register that typically contains the interrupt vector number used
with MC68000 family processor vectored interrupts. Only the host processor can read and write
this register. The contents of the IVR are placed on the host data bus, H[7–0], when both the
and
signals are asserted. The contents of this register are initialized to $0F by a
HREQ
HACK
hardware or software reset. This value corresponds to the uninitialized interrupt vector in the
MC68000 family.
6.7.5 Receive Data Registers (RXH:RXM:RXL)
The host processor views the receive byte registers as three 8-bit read-only registers: the receive
high register (RXH), the receive middle register (RXM), and the receive low register (RXL).
They receive data from the high, middle, and low bytes, respectively, of the HTX register and are
selected by the external host address inputs (HA[2–0]) during a host processor read operation.
The memory address of the receive byte registers are set by ICR[HLEND]. If ICR[HLEND] is
set, the RXH is located at address $7, RXM at $6, and RXL at $5. If ICR[HLEND] is cleared, the
RXH is located at address $5, RXM at $6, and RXL at $7.
When data is transferred from the HTX register to the receive byte register at host address $7, the
ISR Receive Data Register Full (RXDF) bit is set. The host processor can program the RREQ bit
to assert the external HREQ signal when ISR[RXDF] is set. This indicates that the HI08 has a full
word (either 8, 16, or 24 bits) for the host processor. The host processor can program the RREQ
bit to assert the external HREQ signal when ISR[RXDF] is set. Assertion of the HREQ signal
informs the host processor that the receive byte registers have data to be read. When the host
reads the receive byte register at host address $7, the ISR[RXDF] bit is cleared.
Freescale Semiconductor
Reset Value
0
Receive Data Register Full
Indicates that the receive byte registers (RXH:RXM:RXL) contain data
from the DSP56311 to be read by the host processor. RXDF is set when
the HTX is transferred to the receive byte registers. RXDF is cleared
when the host processor reads the receive data register (RXL or RXH
according to HLEND bit). The host processor can clear RXDF using the
initialize function. RXDF can assert the external HREQ signal if the
RREQ bit is set. Regardless of whether the RXDF interrupt is enabled,
RXDF indicates whether the RX registers are full and data can be
latched out (so that the host processor can use polling techniques).
7
6
5
4
IV7
IV6
IV5
IV4
Figure 6-18. Interrupt Vector Register (IVR)
DSP56311 User's Manual, Rev. 2
Description
3
2
1
0
IV3
IV2
IV1
IV0
Host Programmer Model
6-27
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