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VMEchip2

Functional Blocks

The following sections provide an overview of the functions provided by the VMEchip2. See Figure 2-1 for a block diagram of the VMEchip2. A detailed programming model for the local control and status registers (LCSR) is provided in the following section. A detailed programming model for the global control and status registers (GCSR) is provided in the next section.

Local Bus to VMEbus Interface

The local bus to VMEbus interface allows local bus masters access to global resources on the VMEbus. This interface includes a local bus slave, a write post buffer, and a VMEbus master.

Using programmable map decoders with programmable attribute bits, the local bus to VMEbus interface can be configured to provide the following VMEbus capabilities:

Addressing capabilities:

A16, A24, A32

Data transfer capabilities:

D08, D16, D32

The local bus slave includes six local bus map decoders for accessing the VMEbus. The first four map decoders are general purpose programmable decoders, while the other two are fixed and are dedicated for I/O decoding.

The first four map decoders compare local bus address lines A31 through A16 with a 16-bit start address and a 16-bit end address. When an address in the selected range is detected, a VMEbus select is generated to the VMEbus master. Each map decoder also has eight attribute bits and an enable bit. The attribute bits are for VMEbus AM codes, D16 enable, and write post (WP) enable.

The fourth map decoder also includes a 16-bit alternate address register and a 16-bit alternate address select register. This allows any or all of the upper 16 address bits from the local bus to be replaced by bits from the alternate address register. The feature allows the local bus master to access any VMEbus address.

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Motorola MVME172 manual Functional Blocks, Local Bus to VMEbus Interface