3 parallel rom interface, Parallel rom interface, High level scsi scripts mode – Avago Technologies LSI53C876E User Manual
Page 65: Section 2.3, “parallel rom interface
Parallel ROM Interface
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For send data (Data-Out for initiator or Data-In for target), a chained
Block Move instruction indicates that if a partial transfer terminates the
chained block move instruction, the last low-order byte (the partial
memory transfer) should be stored in the lower byte of the
register and not sent across the SCSI bus. Without
the chained Block Move instruction, the last low-order byte would be sent
across the SCSI bus. The starting byte count represents data bytes
transferred from memory but not to the SCSI bus when a partial transfer
exists. For example, if the instruction is an Initiator chained Block Move
Data Out of five bytes (and WSS is not previously set), five bytes are
transferred out of memory to the SCSI controller, four bytes are
transferred from the SCSI controller across the SCSI bus, and one byte
is temporarily stored in the lower byte of the
register waiting to be married with the first byte of the next Block
Move instruction. Regardless of whether a chained Block Move or normal
Block Move instruction is used, if the WSS bit is set at the start of a data
send command, the first byte of the data send command is assumed to
be the high-order byte and is “married” with the low-order byte stored in
the stored in the lower byte of the
register before the two bytes are sent across the SCSI bus. For “N”
consecutive wide data send Block Move commands, the first through the
(Nth – 1) Block Move instructions should be Chained Block Moves.
2.3 Parallel ROM Interface
The LSI53C876 supports up to one megabyte of external memory in
binary increments from 16 Kbytes, to allow the use of expansion ROM
for add-in PCI cards. Both functions of the device share the ROM
interface. This interface is designed for low speed operations such as
downloading instruction code from ROM; it is not intended for dynamic
activities such as executing instructions.
System requirements include the LSI53C876, two or three external 8-bit
address holding registers (HCT273 or HCT374), and the appropriate
memory device. The 4.7 k
Ω
pull-down resistors on the MAD bus require
HC or HCT external components to be used. If in-system Flash ROM
updates are required, a 7406 (high voltage open collector inverter), a
MTD4P05, and several passive components are also needed. The
memory size and speed is determined by pull-down resistors on the
8-bit bidirectional memory bus at power-up. The LSI53C876 senses this