Transmeta Crusoe TM5500, System Design Manual

Page: 94 / 130

July 17, 2002
94
System Design Considerations
6.5.2.2 PLD Pinout
The full pinout of the PLD is described in the following table:
6.5.2.3 PLD Device Selection
The following should be considered when selecting a PLD device to implement the write protection circuit:
• Package . The state machine in the PLD design is very simple, and it could fit into a very small device.
However, an asynchronous flip-flop reset is absolutely necessary for this PLD design to function, and the
smallest PLD with this feature is a 22LV10. For tightly constrained board layouts, Atmel makes a 22LV10
in a 24-pin TSSOP. The Atmel part number is ATF22LV10CZ, and the device’s pinout and fuse map are
the same as in a standard DIP 22LV10.
• Propagation delay . Transmeta successfully tested a part with a 15 ns propagation delay. Although a
slower part may work, Transmeta cannot guarantee it because a slower part was not tested.
• Voltage . The PLD must have 3.3 V outputs because the serial flash ROM is not 5 V-tolerant.
• Power . Since the standard 22LV10 draws at least 70-90 mA from 3.3 V, Transmeta recommends a part
with a power saving feature be used. Many vendors sell 22LV10 parts with power saving features.
Transmeta recommends the Atmel ATF22LV10CZ.
Table 16: PLD Pinout
TSSOP Pin Number Signal Name Signal Description
1 CKIN Serial flash clock input
2 WP Write protect input
3 DIN Serial flash data input
4 PD Power-down pin, implied by device selection
5 CS0IN# Serial flash 0 chip select input
6 CS1IN# Serial flash 1 chip select input (tie high if unused)
7 WPNEG Write protect negate input:
Low = WP is active-high
High = WP is active-low
8 SEL Select serial flash interface input:
Low = Atmel
9, 10, 11 - Unused inputs, tied to ground
12 GND Device ground
13 - Unused input, tied to ground
14, 15, 16 - Unused tri-stated outputs, tied to ground
17 CS0OUT# Serial flash 0 chip select output
18, 19 - Reserved, no connects
20, 21, 22 - Unused tri-stated outputs, tied to ground
23 CS1OUT# Serial flash 1 chip select output (no connect if unused)
24 VCC Device power - connect to 3.3 V
Note
Due to a potential race condition, do not use an ATF22LV10C part for this application.