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33.4. Interface
The following are top level signals from core
| Signal | Width | Direction | Description | 
|---|---|---|---|
| clk | 1 | Input | System Clock | 
| rst_n | 1 | Input | System asynchronous reset. The signal is asserted asynchronously, but is de-asserted synchronously after the rising edge of ssi_clk. The synchronization must be provided external to this component. | 
| Signal | Width | Direction | Description | 
|---|---|---|---|
| avs_read | 1 | Input | Avalon® -MM read control. Asserted to indicate a read transfer. If present, readdata is required. | 
| avs_write | 1 | Input | Avalon® -MM write control. Asserted to indicate a write transfer. If present, writedata is required. | 
| avs_byteenable | dqm_width | Input | Enables specific byte lane(s) during transfer. Each bit corresponds to a byte in avs_writedata and avs_readdata. | 
| avs_address | controller_addr_width | Input | Avalon® -MM address bus. | 
| avs_writedata | sdram_data_width | Input | Avalon® -MM write data bus. Driven by the bus host (bridge unit) during write cycles. | 
| avs_readdata | sdram_data_width | Output | Avalon® -MM readback data. Driven by the altera_spi during read cycles. | 
| avs_readdatavalid | 1 | Output | Asserted to indicate that the avs_readdata signals contains valid data in response to a previous read request. | 
| avs_waitrequest | 1 | Output | Asserted when it is unable to respond to a read or write request. | 
| Signal | Width | Direction | Description | 
|---|---|---|---|
| tcm_grant | 1 | Input | When asserted, indicates that a tristate conduit host has been granted access to perform transactions. tcm_grant is asserted in response to the tcm_request signal and remains asserted until 1 cycle following the deassertion of request. Valid only when pin sharing mode is enabled. | 
| tcm_request | 1 | Output | The meaning of tcm_request depends on the state of the tcm_grant signal, as the following rules dictate: 
 Because tcm_request is deasserted in the last cycle of a bus access, it can be reasserted immediately following the final cycle of a transfer, making both rearbitration and continuous bus access possible if no other hosts are requesting access. Once asserted, tcm_request must remain asserted until granted; consequently, the shortest bus access is 2 cycles. Valid only when pin-sharing mode is enabled. | 
| sdram_dq_width | sdram_data_width | Output | SDRAM data bus output. Valid only when pin-sharing mode is enabled | 
| sdram_dq_in | sdram_data_width | Input | SDRAM data bus input. Valid only when pin-sharing mode is enabled. | 
| sdram_dq_oen | 1 | Output | SDRAM data bus output enable. Valid only when pin-sharing mode is enabled. | 
| sdram_dq | sdram_data_width | Input/Output | SDRAM data bus. Valid only when pin-sharing mode is disabled. | 
| sdram_addr | sdram_addr_width | Output | SDRAM address bus. | 
| sdram_ba | sdram_bank_width | Output | SDRAM bank address. | 
| sdram_dqm | dqm_width | Output | SDRAM data mask. When asserted, it indicates to the SDRAM chip that the corresponding data signal is suppressed. There is one DQM line per 8 bits data lines | 
| sdram_ras_n | 1 | Output | Row Address Select. When taken LOW, the value on the tcm_addr_out bus is used to select the bank and activate the required row. | 
| sdram_cas_n | 1 | Output | Column Address Select. When taken LOW, the value on the tcm_addr_out bus is used to select the bank and required column. A read or write operation will then be conducted from that memory location, depending on the state of tcm_we_out. | 
| sdram_we_n | 1 | Output | SDRAM Write Enable, determines whether the location addressed by tcm_addr_out is written to or read from. 0=Read 1=Write | 
| sdram_cs_n | Output | SDRAM Chip Select. When taken LOW, will enables the SDRAM device. | |
| sdram_cke | 1 | Output | SDRAM Clock Enable. The SDRAM controller does not support clock-disable modes. The SDRAM controller permanently asserts the tcm_sdr_cke_out signal on the SDRAM. |