16-24
DSP56853/854/855/857/858 User’s Manual
MOTOROLA
Preliminary
Servicing the Host Interface
16
address without affecting the internal state of the HI8, useful if the user desires to access
all of the HI8 registers by stepping through the HI8 addresses. The ISR can not be
accessed by the DSP core. The status bits are described in the following paragraphs.
Figure 16-10. Interface Status Register (ISR)
16.10.1.1 Reserved—Bits 15–8
These bits are reserved or not implemented. They are read as, and written with 0s.
16.10.1.2 Host Request (HREQ)—Bit 7
This bit indicates the status of the external Host Request (HREQ) output pin if the HRMS
bit is cleared; or the external Host Transmit Receive Request (HTRQ) output pins, and
HRRQ respectively, if HRMS is set. When the HREQ status bit is cleared, it indicates the
Host Request pin, HREQ or HTRR, HTRQ and HRRQ, are deasserted and either Host
Processor interrupts or host DMA transfers are being requested.
If the HREQ status bit is set, it means the Host Request (HREQ) pin, the Host Transmit
Request (HTRQ), or Host Receive Request (HRRQ) are asserted, indicating the DSP is
interrupting the Host Processor or a Host DMA transfer request is being made. The HREQ
interrupt request may originate from one or more of two sources:
1. The receive byte registers are full
2. The transmit byte registers are empty
These conditions are indicated by the Interrupt Status Register (ISR) RXDF and TXDE
status bits, respectively. If the interrupt source has been enabled by the associated request
enable bit in the Interface Control Register (ICR); HREQ, HTRQ, or HRRQ bits is set if
one or more of the two enabled interrupt sources is set. DSP reset clears HREQ.
16.10.1.3 Host DMA Status (DMA)–Bit 6
The DMA status bit (DMA) indicates that the Host Processor has enabled the DMA mode
of the HI8 (HM1 or HM0 =1). When the DMA status bit is clear, it indicates that the DMA
mode is disabled by the Host mode bits (HM0 and HM1) in the Interface Control Register
ICR and no DMA operations are pending. When DMA is set, it indicates that the DMA
$1FFFD8 + $2
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
Read
0
HREQ
DMA
0
HF3
HF2
TRDY
TXDE RXDF
Write
0
RESET
0
00000
0