GPMC
7.1.3.3.9.4 OEn/REn: Output Enable / Read Enable Signal Control Assertion / Deassertion Time
(OEONTIME / OEOFFTIME / OEEXTRADELAY / OEAADMUXONTIME / OEAADMUXOFFTIME)
The GPMC_CONFIG4_i[3-0] OEONTIME field defines the OEn_REn signal assertion time relative to start
access time. It is applicable only to read accesses.
The GPMC_CONFIG4_i[12-8] OEOFFTIME field defines the OEn_REn signal deassertion time relative to
start access time. It is applicable only to read accesses. OEn_REn is not asserted during a write cycle.
OEONTIME, OEOFFTIME, OEAADMUXONTIME and OEAADMUXOFFTIME parameters are applicable to
synchronous and asynchronous modes. OEONTIME can be used to control an address and byte enable
valid setup time control before OEn_REn assertion. OEOFFTIME can be used to control an address and
byte enable valid hold time control after OEn_REn assertion.
OEAADMUXONTIME and OEAADMUXOFFTIME parameters have the same functions as OEONTIME
and OEOFFTIME, but apply to the first OE assertion in the AAD-multiplexed protocol for a read phase, or
to the only OE assertion for a write phase. It is the user responsibility to make sure OEAADMUXOFFTIME
is programmed to a value lower than OEONTIME. Functionality in AAD-mux mode is undefined if the
settings do not comply with this requirement. OEAADMUXOFFTIME shall never be equal to OEONTIME
because the AAD-mux protocol requires a second address phase with the OEn signal de-asserted before
OEn can be asserted again to define a read command.
The OEn_REn signal transitions as controlled through OEONTIME, OEOFFTIME, OEAADMUXONTIME
and OEAADMUXOFFTIME can be delayed by half a GPMC_FCLK period by enabling the
GPMC_CONFIG4_i[7] OEEXTRADELAY bit. This half of a GPMC_FCLK period provides more granularity
on OEn_REn assertion and deassertion time to assure proper setup and hold time relative to GPMC_CLK.
If enabled, OEEXTRADELAY applies to all parameters controlling OEn_REn transitions.
OEEXTRADELAY must be used carefully, to avoid control-signal overlap between successive accesses to
different chip-selects. This implies the need to program RDCYCLETIME and WRCYCLETIME to be
greater than OEn_REn signal-deassertion time, including the extra half-GPMC_FCLK-period delay.
When the GPMC generates a read access to an address-/data-multiplexed device, it drives the address
bus until OEn assertion time.
7.1.3.3.9.5 WEn: Write Enable Signal Control Assertion / Deassertion Time (WEONTIME / WEOFFTIME /
WEEXTRADELAY)
The GPMC_CONFIG4_i[19-16] WEONTIME field (where i = 0 to 3) defines the WEn signal-assertion time
relative to start access time. The GPMC_CONFIG4_i[28-24] WEOFFTIME field defines the WEn signal-
deassertion time relative to start access time. These bit fields only apply to write accesses. WEn is not
asserted during a read cycle.
WEONTIME can be used to control an address and byte enable valid setup time control before WEn
assertion. WEOFFTIME can be used to control an address and byte enable valid hold time control after
WEn assertion.
WEn signal transitions as controlled through WEONTIME, and WEOFFTIME can be delayed by half a
GPMC_FCLK period by enabling the GPMC_CONFIG4_i[23] WEEXTRADELAY bit. This half of a
GPMC_FCLK period provides more granularity on WEn assertion and deassertion time to guaranty proper
setup and hold time relative to GPMC_CLK. If enabled, WEEXTRADELAY applies to all parameters
controlling WEn transitions.
The WEEXTRADELAY bit must be used carefully to avoid control-signal overlap between successive
accesses to different chip-selects. This implies the need to program the WRCYCLETIME bit field to be
greater than the WEn signal-deassertion time, including the extra half-GPMC_FCLK-period delay.
277
SPRUH73H – October 2011 – Revised April 2013
Memory Subsystem
Copyright © 2011–2013, Texas Instruments Incorporated