BRIGHT
Preliminary BM29F400T/BM29F400B
Microelectronics
Inc.
- 8 -
If the device is deselected during programming or erase, the device will draw active current until the
programming or erase operation is completed. In the standby mode the outputs are in a high
impedance state, independent of the OE input.
Output Disable Mode
With the OE input at a logic high level (VIH), output from the device is disabled. This will cause the
output pins to be in a high impedance state. It is shown in Table 1 that CE = VIL and WE = VIH for
Output Disable. This is to differentiate Output Disable mode from Write mode and to prevent
inadvertent writes during Output Disable.
Program and Erase Modes
Device programming and erase are accomplished via the command register. Contents of the register
serve as inputs to the internal state machine. Outputs of the state machine dictate the function of the
device.
The command register itself does not occupy any addressable memory locations. The register is a
latch used to store the commands along with the addresses and data information needed to execute
the command. The command register is written by bringing WE to VIL, while CE is at VIL and OE is
at VIH. Addresses are latched on the falling edge of WE or CE , whichever happens later, while data
is latched on the rising edge of WE or CE , whichever happens first. Standard microprocessor write
timings are used. Refer to AC Characteristics for Programming/Erase and their respective Timing
Waveforms for specific timing parameters.
Enable Sector Protect and Verify Sector Protect Modes
The BM29F400 has a hardware Sector Protect mode that disables both Programming and Erase
operation to the protected sector(s). There are total of 11 sectors in this device. The sector protect
feature is enabled using the programming equipment at the user's site. The device is shipped from
the BMI factory with all sectors unprotected.
To verify programming of the protection circuitry, the programming equipment must force VID on the
address pin A9 with CE and OE at VIL and WE at VIH. As shown in Table 2, scanning the sector
addresses while (A6, A1 and A0) = (0, 1, 0) will produce a 01H code at the device output pins for a
protected sector. In the Verify Sector Protect mode, the device will read 00H for an unprotected
sector. In this mode, the lower order addresses, except for A0, A1 and A6, are don't care. Address
locations with A1 = VIL are reserved for Electronic ID manufacturer and device codes. It is also
possible to determine if a sector is protected in-system by writing the Electronic ID command
(described in the Electronic ID command section below.)
Temporary Sector Unprotect Mode
The BM29F400 has a Temporary Sector Unprotect feature that allows the protect feature to be
temporarily suspended to change data in a protected sector in-system. The Temporary Sector
Unprotect mode is activated by setting the RESET pin to VID (11.5V - 12.5V).
In this mode, protected sectors can be programmed or erased by selecting the sector addresses.
Once VID is removed from the RESET pin, all previously protected sectors will be protected. Refer to
the Temporary Sector Unprotect algorithm and timing waveforms.
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