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0453H–PLD–7/05

ATF16V8CZ

8.

Macrocell Configuration

Software compilers support the three different OMC modes as different device types. These

device types are listed in the table below. Most compilers have the ability to automatically select

the device type, generally based on the register usage and output enable (OE) usage. Register

usage on the device forces the software to choose the registered mode. All combinatorial out-

puts with OE controlled by the product term will force the software to choose the complex mode.

The software will choose the simple mode only when all outputs are dedicated combinatorial

without OE control. The different device types listed in the table can be used to override the

automatic device selection by the software. For further details, refer to the compiler software

manuals.

When using compiler software to configure the device, the user must pay special attention to the

following restrictions in each mode.

In registered mode pin 1 and pin 11 are permanently configured as clock and output enable,

respectively. These pins cannot be configured as dedicated inputs in the registered mode.

In complex mode pin 1 and pin 11 become dedicated inputs and use the feedback paths of pin

19 and pin 12 respectively. Because of this feedback path usage, pin 19 and pin 12 do not have

the feedback option in this mode.

In simple mode all feedback paths of the output pins are routed via the adjacent pins. In doing

so, the two inner most pins (pins 15 and 16) will not have the feedback option as these pins are

always configured as dedicated combinatorial output.

8.1

ATF16V8CZ Registered Mode

PAL Device Emulation/PAL Replacement. The registered mode is used if one or more regis-

ters are required. Each macrocell can be configured as either a registered or combinatorial

output or I/O, or as an input. For a registered output or I/O, the output is enabled by the OE pin,

and the register is clocked by the CLK pin. Eight product terms are allocated to the sum term.

For a combinatorial output or I/O, the output enable is controlled by a product term, and seven

product terms are allocated to the sum term. When the macrocell is configured as an input, the

output enable is permanently disabled.

Any register usage will make the compiler select this mode. The following registered devices can

be emulated using this mode:

16R8

16RP8

16R6

16RP6

16R4

16RP4