
MachXO2 Programming and Configuration Usage Guide
19
Figure 8. Default JTAG Port with JTAG_PORT = ENABLE
The JTAG port can become general purpose I/O. By setting the JTAG_PORT preference in the Diamond Spread-
sheet View to the DISABLE state. When the JTAG port is in the DISABLE state the JTAGENB pin becomes a dedi-
cated input. Driving the JTAGENB low disables the JTAG port and the four JTAG pins become general purpose
I/Os. Driving the JTAGENB input high enables the JTAG port. Figure shows JTAG port behavior under the control
of the JTAGENB.
Figure 9. JTAG Port Behavior with JTAG_PORT = DISABLE
It is critical when using the JTAGENB feature that logic attached to the JTAG I/O pins not contend with a JTAG program-
ming system. The external logic must ignore any JTAG transactions performed by an external programming system.
Lattice parallel port or USB download cables provide an output called ispEN. The ispEN signal can be attached to the
JTAGENB input to control the availability of the JTAG port. An alternate mechanism to control the JTAGENB input is to
use a shunt that can be installed or removed as required.
Configuration Modes
The MachXO2 provides multiple options for loading the configuration SRAM from a non-volatile memory. The previ-
ous section described the physical interface necessary to interact with the MachXO2 configuration logic. This sec-
tion focuses on describing the functionality of each of the different configuration modes. Descriptions of important
settings required in the Diamond Spreadsheet View are also discussed.
SDM Mode
Self Download Mode is the primary configuration method for the MachXO2. The advantages of Self Download
Configuration Mode include:
•
Speed
: The MachXO2 is ready to run in a few milliseconds depending on the density of the device.
•
Security
: The configuration data is never seen outside the device during the load to SRAM. You can prevent the
internal memory from being read.
•
Reduced cost
: There is no need to purchase a PROM specifically reserved for programming the MachXO2.
•
Reduced board space
: Elimination of an external PROM allows your board to be smaller.
•
Improved reliability
: The MachXO2 can boot from an external PROM if the internal Flash memory gets cor-
rupted during a system update.
TCK/IO
TMS/IO
TDI/IO
TDO/IO
TCK
TMS
TDI
TDO
MachXO2
IO/JTAGE
N
B
TCK/IO
TMS/IO
TDI/IO
TDO/IO
I/O
I/O
I/O
I/O
IO/JTAGE
N
B
TCK/IO
TMS/IO
TDI/IO
TDO/IO
JTAGE
N
B = ‘1’
TCK
TM
TDIS
TDO
V
CCIO
MachXO2
MachXO2
G
N
D
JTAGE
N
B = ‘0’