83Plus:Ports:14

This port is protected, which means user programs cannot ordinarily write to it directly.

Synopsis

Port Number: 14h

Function: Flash Write-Lock Control

Writing to this port controls whether or not the Flash ROM chip will accept write/erase instructions. However, writes are only accepted after the unlock sequence is executed from a protected page.

Read Values

• 83+ Basic only: Mirror of port 04h.
• 83+ SE/84+ only: Reads 0 zero.

Write Values

• Write 00h to lock the flash. Write 01h to unlock it.

Comments

When the flash chip is locked, then write/erase instructions are rejected. In addition, protected pages cannot be read. There is only one protected page. On the normal 83+, this is page 1Eh. On the normal 84+, it is 3Eh. On the 83+ SE and 84+ SE it is 7Eh. This page holds the certification data, which includes ID number, validation number, application authorizations, public keys, and other related data.

Use bit 2 of port 2 to check if flash is unlocked.

Other protected ports may be written to from any area (unprivileged ROM, RAM, etc) without requiring a special sequence once Flash is unlocked.