Rainbow Electronics AT6010LV - Manual (Page 8)

AT6000(LV) Series
8
Figure 11. A-type I/O Logic
Figure 12. B-type I/O Logic
TTL/CMOS Inputs
A user-configurable bit determines the threshold level –
TTL or CMOS – of the input buffer.
Open Collector/Tristate Outputs
A user-configurable bit which enables or disables the active
pull-up of the output device.
Slew Rate Control
A user-configurable bit controls the slew rate – fast or slow
– of the output buffer. A slow slew rate, which reduces
noise and ground bounce, is recommended for outputs that
are not speed-critical. Fast and slow slew rates have the
same DC-current sinking capabilities, but the rate at which
each allows the output devices to reach full drive differs.
Pull-up
A user-configurable bit controls the pull-up transistor in the
I/O pin. It’s primary function is to provide a logical “1” to
unused input pins. When on, it is approximately equivalent
to a 25K resistor to V
CC
.
Enable Select
User-configurable bits determine the output-enable for the
output driver. The output driver can be static – always on or
always off – or dynamically controlled by a signal gener-
ated in the array. Four options are available from the array:
(1) the control is low and always driving; (2) the control is
high and never driving; (3) the control is connected to a ver-
tical local bus associated with the output cell; or (4) the
control is connected to a horizontal local bus associated
with the output cell. On power-up, the user I/Os are config-
ured as inputs with pull-up resistors.
In addition to the functionality provided by the I/O logic, the
entrance and exit cells provide the ability to register both
inputs and outputs. Also, these perimeter cells (unlike inte-
rior cells) are connected directly to express buses: the
edge-facing A and B outputs of the entrance cell are con-
nected to express buses, as are the edge-facing A and B
inputs of the exit cell. These buses are perpendicular to the
edge, and provide a rapid means of bringing I/O signals to
and from the array interior and the opposite edge of the
chip.
Chip Configuration
The Integrated Development System generates the SRAM
bit pattern required to configure a AT6000 Series device. A
PC parallel port, microprocessor, EPROM or serial configu-
ration memory can be used to download configuration
patterns.
Users select from several configuration modes. Many fac-
tors, including board area, configuration speed and the
number of designs implemented in parallel can influence
the user’s final choice.
Configuration is controlled by dedicated configuration pins
and dual-function pins that double as I/O pins when the
device is in operation. The number of dual-function pins
required for each mode varies.