Bit manipulation using opcodes

How to update a bit using opcode

This guide will show you how to manipulate bits in SEEM. Before you read on, you must have already read this guide about motorola opcode. As you can see from the "motorola opcode" guide, we can only read/write bytes, but not bits. We have to do some calculation, in order to change only the bits we want to change.

I think the best way to explain it is by example. Let's say we want to do the following seem edit:

option to switch storage device (discovered by Yuet)
SEEM 0032-0001 offset 9F bit 3:
on = switch to phone memory/memory card directly in list, java apps will be installed in card when "install new apps"
off = press menu key to see "switch storage device" option, will prompt to select storage device when "install new apps"

Steps:

1. to get the value of the offset 9F in SEEM 0032-0001, we use the following opcode:
32*50*1*159*1

2. The value we get is "c8", which is a hex value. It is 200 in dec value. We try to decode "200" using this formula:
200 = bit0 x 1 + bit1 x 2 + bit2 x 4 + bit3 x 8 + bit4 x 16 + bit5 x 32 + bit6 x 64 + bit7 x 128

What we get is:
200 = 0 x 1 + 0 x 2 + 0 x 4 + 1 x 8 + 0 x 16 + 0 x 32 + 1 x 64 + 1 x 128

so we can see in this offset, bit 3, 6 & 7 are on. In this example, we want to turn off bit 3 to enable the "switch storage device" option, so we change value of bit3 to 0 in the formula. We get:
0 x 1 + 0 x 2 + 0 x 4 + 0 x 8 + 0 x 16 + 0 x 32 + 1 x 64 + 1 x 128 = 192

192 is the value we are going to write to the offset 9F.

3. We write the value 192 to offset 9F in SEEM 0032-0001 using the following opcode:
47*50*1*159*1*192

4. Reboot the phone using opcode 34, and it is done.

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