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DSP56853/854/855/857/858 User’s Manual
MOTOROLA
Preliminary
Servicing the Host Interface
16
16.10.1.9 Receive Data Register Full (RXDF)—Bit 0
Setting the Receive Data Register Full (RXDF) flag bit indicates the receive byte registers
(RXH and RXL) contain data from the DSP Side and can be read by the Host Processor.
The RXDF bit is set when the HTX is transferred to the receive byte registers. RXDF is
cleared when the receive data (RXL or RXH according to HLEND bit) register is read by
the Host Processor. RXDF can be cleared by the Host Processor using the initialize
function. RXDF may be used to assert the external HREQ pin if the RREQ bit is set.
Regardless of whether the RXDF interrupt is enabled, RXDF provides valid status so
polling techniques may be used by the Host Processor.
16.10.2 Interrupt Vector Register (IVR)
The Interrupt Vector Register (IVR) is an 8-bit read/write register typically containing the
interrupt vector number used with MC68000 family processor vectored interrupts. Only
the Host Processor can read and write this register. The contents of IVR are placed on the
Host data bus (H0–H7) when both HREQ and HACK pins are asserted and Host DMA is
not enabled. The contents of this register are initialized to a pre-defined value by a
hardware or software reset, corresponding to the uninitialized interrupt vector in the
MC68000 family.
Figure 16-11. Interrupt Vector Register (IVR)
16.10.3 Receive Byte Registers (RXH, RXL)
The Receive Byte Registers are viewed as two 8-bit read-only registers by the Host
Processor. These registers are called Receive Data High (RXH) and Receive Data Low
(RXL). These two registers receive data from the High Byte and Low Byte, respectively
from the HTX register. They are selected by three external Host Address (HA2, HA1, and
HA0) inputs during a Host Processor read operation or by an on-chip address counter in
DMA operations. The Receive Byte Registers contain valid data when the Receive Data
Register Full (RXDF) bit is set. The Host Processor may program the RREQ bit to assert
the external HREQ pin when the RXDF bit is set. This informs the Host Processor or Host
DMA controller of the Receive Byte Registers full condition. Reading the Data Register at
Host Address $7 clears the RXDF bit.
$1FFFD8 + $3
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
Read
0
IV7IV6
IV5IV4
IV3IV2
IV1IV0
Write
0
RESET
000000000000
0000