CobraNet
TM
EV-2
Page 11
Port 3:
Interfacing the Microcontroller to the CM
Please refer to the EV-2 schematic, found in
Appendix D
for information regarding interfacing to the
CM.
The CM has a host interface that allows a host processor (such as an 8051 microcontroller) to interface
to the DSP on the CM. From a hardware perspective the interface to the CM-1 and CM-2 is almost the
same,. The host interface signals are a data strobe signal, HDS#; a read/write line, HRW, an 8-bit
bi-directional data bus, HD0-HD7, and three address lines, HA0-HA2 on the CM-1 and four address
lines, HA0-HA3 on the CM-2. The HEN# line has been configured by the CobraNet software to be
ignored or seen as a logic low. Given this host configuration, the interface of the microcontroller to the
CM host port is straightforward. In addition to the above signals there are two more, HACK# and
HREQ# which can be used as flags to indicate a state change on the CM.
With regard to the CM-1 which uses a Motorola DSP56303, care must be taken with the timing of
HDS# and HWR. Motorola's timing specifications for the DSP56303 host port in a non-multiplexed,
single data strobe mode requires a set up time from the falling edge of HWR# to the falling edge of
HDS# of 4.7ns and the hold time from the rising edge of HDS# to the rising edge of HWR# of 3.3ns.
The pulse of the HDS# signal must be wholly within the pulse of the HWR# signal with the constraints
stated above. Please refer to Motorola's DSP56303 Technical Data sheet for complete information
regarding timing and interface issues. This is available for download from the Motorola web site at
http://www.motorola.com/SPS/DSP/.
Bit #
Name of Signal
I/O
Description
0
RXD
I
RS232 serial port receive signal.
1
TXD
O
RS232 serial port transmit signal
2
HREQ#
O
Connected to the CM module host
request signal. See CobraNet Techni-
cal Datasheet for a complete descrip-
tion of this signal.
3
HACK#
I
Connected to the CM module host
acknowledge signal. See CobraNet
Technical Datasheet for a complete
description of this signal. May be
used as an interrupt request on the
microcontroller.
4
Watchdog
I
Watchdog signal from the CM
5
MCU_P35
I/O
Connected to SCI_CLK via the
FPGA.
6
WR#
O
Microcontroller write signal.
7
RD#
O
Microcontroller read signal.
Table 5: Port 3 Signal Descriptions
