Computer Hardware User Manual

VIPER Technical Manual Detailed hardware description

To write to OUT[0:7], write to the following PXA255 processor GPIO lines to drive the

outputs.

VIPER outputs PXA255 GPIO

OUT0 GPIO20

OUT1 GPIO21

OUT2 GPIO22

OUT3 GPIO23

OUT4 GPIO24

OUT5 GPIO25

OUT6 GPIO26

OUT7 GPIO27

The PXA255 GPIO lines must be configured using the registers built into the device to

ensure they function correctly. RedBoot configures GPIO20 – GPIO27 as outputs, and

sets OUT0 to logic ‘0’, and OUT1 – 7 as logic ‘1’. Eboot cannot set these up as outputs

as it only boots the Windows CE image. Once Windows CE is booted you can simply

write to a mapped address. For an example of how to do this under Windows CE

please see the Windows CE Technical Manual.

Please note:

• IN0-7 cannot be configured as outputs as they are hardwired as input-only

by a buffer.

• OUT0-7 cannot be configured as inputs as they are hardwired as

output-only by a buffer.

• OUT6-7 are not available if the VIPER is fitted with the TPM IC.

The GPIO lines are programmed using the GPCR0 and the GPSR0 to set the line to ‘0’

or ‘1’ respectively. The registers are 32-bit wide and bits 20-27 relate to GP20-27. To

set one of the GP20-27 signals to a logic ‘1’ write a ‘1’ to the corresponding GPSR0 bit.

To set one of the GP20-27 signals to a logic ‘0’ write a ‘1’ to the corresponding GPCR0

bit. To monitor the current state of a GP20-27 signal line read from GPLR0. A read-

modify-write operation to GPLR0 will not change the state of the GP20-27 signal lines.

GPLR0 0x40E00000

GPSR0 0x40E00018

GPCR0 0x40E00024

PXA255

Transceiver

PL9

GPIO[20:27]

OUT[0:7]

OUT0B