Host Interface (15 Pins) - Motorola DSP56156 Manual

2.6

HOST INTERFACE (15 PINS)

H0-H7 (Host Data Bus) - This bidirectional data bus is used to transfer data between
the host processor and the DSP. This bus is an input unless enabled by a host
processor read. H0-H7 may be programmed as general purpose parallel I/O
pins called PB0-PB7 when the Host Interface (HI) is not being used.
HA0-2 (Host Address 0-2) - These inputs provide the address selection for each HI reg-
ister and are stable when HEN is asserted. HA0-HA2 may be programmed as
general purpose parallel I/O pins called PB8-PB10 when the HI is not being used.
(Host Read/Write) - This input selects the direction of data transfer for each
HR/W
host processor access. If HR/W is high and HEN is asserted, H0-H7 are outputs
and DSP data is transferred to the host processor. If HR/W is low and HEN is
asserted, H0-H7 are inputs and host data is transferred to the DSP. HR/W is
stable when HEN is asserted. HR/W may be programmed as a general purpose
I/O pin called PB11 when the HI is not being used.
HEN (Host Enable) - This input enables a data transfer on the host data bus. When
HEN is asserted and HR/W is high, H0-H7 becomes an output and DSP data
may be latched by the host processor. When HEN is asserted and HR/W is low,
H0-H7 is an input and host data is latched inside the DSP when HEN is deas-
serted. Normally a chip select signal derived from host address decoding and
an enable clock is connected to the Host Enable. HEN may be programmed as
a general purpose I/O pin called PB12 when the HI is not being used.
(Host Request) - This open-drain output signal is used by the HI to request ser-
HREQ
vice from the host processor. HREQ may be connected to an interrupt request
pin of a host processor, a transfer request of a DMA controller, or a control input
of external circuitry. HREQ is asserted when an enabled request occurs in the
HI. HREQ is deasserted when the enabled request is cleared or masked, DMA
HACK is asserted, or the DSP is reset. HREQ may be programmed as a gen-
eral purpose I/O pin (not open-drain) called PB13 when the HI is not being used.
HACK (Host Acknowledge) - This input has two functions - (1) to provide a Host Ac-
knowledge signal for DMA transfers or (2) to control handshaking and to pro-
vide a Host Interrupt Acknowledge compatible with MC68000 family
processors. If programmed as a Host Acknowledge signal, HACK may be used
as a data strobe for HI DMA data transfers. If programmed as an MC68000
Host Interrupt Acknowledge, HACK is used to enable the HI Interrupt Vector
Register (IVR) onto the Host Data Bus H0-H7 if the Host Request HREQ output
MOTOROLA
HOST INTERFACE (15 PINS)
DSP56156 PIN DESCRIPTIONS 2 - 11